Damn I need some help!

Alright, this is long but please read, a friend of mine bought an s10 that was already fully bagged, very nicely done I might add, it isn't a hack job or anything and from what I understand it was done by a reputable shop. A while back the compressors began acting up, like they weren't running at full power (it had 2 450's on it), then they began running extremely slow and one sounded like it was dieing, so he brings it to us and decides it's time for a update on his setup and wants to switch out the comps, we put a set of 460's on it, new watertraps new pressure switches, new switchbox. Everything started out working fine, the new comps started slowly doing the same thing over again, now they run worse than the 450's and are barely pumping, his batteries are brand new (optimas) no fuses are blown, but they are running off solenoids, could these be the case or what, I've tried testing and swapping everything but them. We didn't do the install so its extremly hard to trace anything back on this truck, the guys that did it did a damn good job of hiding stuff, has anyone else had this problem or can lead me in a direction, sorry about the book

check the voltage goin into the solenoid and comin out of the solenoid. usually when a solenoid gets old they start to rust inside and the copper wire runnin around the coil gets froze up and starts gettin hard to move in there.. i'll bet there is a significant voltage drop comin out of the solenoid. most likely that is the entire problem. on rare occasions, the wire runnin from the batt to the solenoid could be bad. if it is a small wire, it generates heat when you are tryin to pull that much current through it and the copper wire will actually atart to lose it conductivity. but that usually takes years of gettin hot and runnin hard. but with dual compressors that size i reccomend AT LEAST 4guage wire from the battery. it never hurts to overshoot and get too big of a wire. it wont hurt you a bit to have 2guage, but most likely the problem lies in the solenoid

I appreciate it man, I was thinking that but wanted to be sure, I've never had this problem. I've checked it before and it looked good, but you never know, all wire is 4 gauge wire, and I've replaced it when I put his new comps in so I know its good, again I appreciate it.