Leveling my truck

[Evs-One]

IT seems that ever since I installed my Brothers' Trucks springs, my truck seems to lean to the drivers' side more. I have at most 5k miles and probably 4 years on the springs. Before, I had the front coils cut and the rears heated evenly, and the truck seemed decently level. It's really starting to bug me. I know for a fact this truck was never in a major accident...just fender benders and such(it's a 70 C-10 btw). I installed new poly cab mounts and ended up shimming the drivers side slightly to at least line up the body lines on the cab with those on the bed- the cab use to sag more on drivers side. So now, the truck is about 1/2" to 1" lower on the driver side than the passenger side, but the cab is finally even with the bed. I was thinking it's either the frame or suspension. Any ideas what to check?? Appreciate it