2002 Silverado 2500hd Runs Rough And Hesitates After 2k Rpms

[vr666dub]

I have a 2002 silverado 2500 hd with the 6.0 gas motor. Just a couple days ago my truck started stumbling and or had no power while I was towing my trailer. The next day the check engine lite came in and it wa ok101 the mass air. So I went and bought one, put it in and it still acts the same...the same code cam back. So I read on here that a guy had a problem with the evap o ring..I checked mine and yes it was lose, so I put a new o ring on and the light went out but still runs like crap. I know some people say clogged cats but I've had them in cars before and its not that, some may say fuel pump..but I wanna make sure before I send a couple hundred.... I did notice that it will seem fine taking off but when I hit 2000 rpms its falls on its face , and wot dosnt do anything..it just downshifts and sounds like its pinging. The evap was making a lot of noise and it sounds like there might be and air leak but I sprayed started fluid and nothing happen.. it also surges when pulling the trailer up hills like its trying to run normal then messed up then normal then messed up...don't really wanna take it to the dealer...any idea and info would be great....thanks for looking..

[GMstrong]

check fuel pressure