So here it goes

After my polymer 80 build was complete I took it to the range for the first time.  About every 4 or 5 rounds, the slide fails to go back into full battery which then causes a light strike on the next round.  Watched several videos before building that addressed more commonly know problems and made sure to sand down the metal slide parts before completing my build.  Used increasingly fine grits of sand paper.  I also notice that when I assemble the slide to the lower, I have to manually pull down the slide release to get the slide to move back to the rear rails.  Used a Brownells glock 19 gen 3 completion kit if that matters.  Should I try and aftermarket recoil spring with different spring rates?  Or should I keep shooting till it smooths out.  Only have about 150 rounds through it.  Not sure which direction to take.  Any help is appreciated.

Which P80 are you talking about? 17 V1 or V2? Or 19 (PF940c. only comes in V2)?
I've built two PF940c's (as said, all 940c's are V2) and the slide release does not contact the slide unless either an empty mag is pushing it up, or you're manually manipulating it up (although the lever does not rest bottomed out against the frame as factory Glocks do).
If you're talking about the PF940c, there are a couple of culprits. One is the rear rail (and it's height relative to the front rail). If that rail is out of spec, or the hole was not drilled in exactly the right spot, you'll surely have issues (one of which is as you describe, if the hole is drilled too low).
Definitely going to need more details to help you out.

ETA: if you're talking V2's, I'll add some advice: disregard a lot of advice you'll get.
For starters, if you're rails are too tight in the slide, do NOT sand/file on them. IF they are too tight, it's because the rear rail stamping had it's outward angles placed too low (which is why the outward tabs are too long, thus making it too tight, width wise) in the slide), which also places the curve too low (remember, it's a stamping, so if it's too wide, it's also too low. The overall stamping starts out as one long piece, so the bends and height are directly correlated to each other. If one is off, so is the other). If it is riding too low, you get what you described. If the rear rail is out of spec (does not fit slide properly), do NOT touch it, let P80 know (it's a common issue) and they will happily replace that rear rail (they refer to it as the RMA) with a hand inspected one (I know, I've been through that replacement on one of them. And that immediately resolved the fitment issue).
Second common issue. The slide lock lever spring does NOT fit properly into the frame. They did not make the vertical slot deep enough. You'll want to snip just the curve off the spring leg (about 1/32- 1/16" of the end). It will then lay flat into the spring channel and will not impede your recoil spring (it will fit like it does in Glocks, after you slightly shorten the "leg").
Third common issue: Don't be shy about cutting out the recoil spring/guide rod channel. Go well into the "line" and a tad past. The lower should blend seamlessly to the area of the slide lock spring (no ledge). If you have a ledge or bump, your spring will scrape and drag. You'll not hurt anything by going past that line, so go past that line.
Fourth common issue: on the RMA (rear module assembly, or "rear rail", before you install it, deburr the two stamping lines on the rear curve where the trigger bar would stop/bottom out at. If you do not, your trigger will short itself and not work reliably. Take a file, and totally remove those two stamping lines/burrs.

Hope this helps! (of course, if you're not talking about V2's.. then just ignore this post )

I'm sorry for the confusion.  The slide lock is what has to be pressed down when installing the slide.  Not the slide release.  And it is a glock 19 build.

Ahh. easy fix. See my edited above post. Pay attention to the slide lock spring issue mentioned.

Put a little light oil in the grooves on the slide that the rails slide in. Fire away until it breaks in. Oil as needed until not needed.
Also. Take black marker and color the top of the rear frame rails. Then work the slide back and forth several times and see where the high spots are. Then file the high spots down a little.
see if that helps. Its what I did. What # spring did you say you had in it? Just curious.

Not sure what spring honestly.  It came with the Brownells completion kit

so it's not an issue with the take down lever?

a lot of times that little spring that goes into the front part of the frame that actuates the take down lever sticks out a bit. it has to go in just right to sit flush. have you compared it to a regular glock?

I thought this was a handy tip for prepping and leveling out the frame rails:

Polymer 80 PF940C rail quick tip

Yeah it is probably the take down lever.  I remember having to force it in during the build. I took a hard look at the spring and see that its rubing on something.  I'm going to start there and see what happens when I get a day off.

if you look at the take down spring on a factory glock, it sits flush in the frame. that was probably the hardest piece to get in right in the poly 80. i'd bet yours sticks up a little and produces a little hump. mess around with it to get it flush. it's a PITA but once it's in you should be GTG.

Ok.  Snipped the spring for the take down lever and also polished the take down lever as there was some wear Mark's on top.  After dry firing it for a bit, I notice that if I pull the trigger and hold it back, and then pull back on the slide to reset the trigger the slide will not go all the way forward into full battery until I let up on the trigger a bit.  If I pull the slide all the way back and release it, it will go into full battery.  I have not gone back to the range yet but it feels like something is binding a bit.  It might be something that will work itself out with more rounds down range but anyone have any ideas what might cause this?