Sounds like you had some pins that might have been out of spec. I have 2 PSA LPKs and the triggers are completely different. The first one was smooth as can be and had a nice crisp break. The second feels like someone duped a shovel full of sand into my lower. That's the only issue I've had in assembling lowers though and it's not really an issue. If you get quality parts that are in spec, you should be fine and not run into problems.
On a side note, my first AR is an M&P and then I assembled a Spike's lower with PSA kit. I did however get a complete Spike's upper to slap on it. They make a great pair!