hey guys i need some thoughts or advice. i took the truck to town last night and on my way home about 11pm i decided i wanted to see what the truck would do. so from about a 55 roll i stuffed it in 3rd held it. shifted 4th and when i hit 100 or so there was a really loud, strong vibration up through the shifter... the driveline on this thing has been an absolute nightmare... from blowing u joints and denting drive shafts. etc etc. etc. here's is what i have done to try to correct the issue 2 weeks ago...

i put a magnetic degree finder on the rear end while on a lift and it gave me -10 degrees... obviously off if its supposed to be -3... well i had already gotten 4 degree shims so i put them in. put the truck on the ground and with all the weight on the suspension it read a -5... still off i know... ive driven the truck 250 miles and i have put a driveshaft from a 98 c-1500 auto 4.3 in it and it FIT PERFECT there was plenty of clearance on the front yoke and i have a brand new ujoint in the rear. the drive shaft has no dents in it and i HAVE NO CLUE WTF THE PROBLEM IS. i know -5degress is not -3 but would it really cause that much vibration? could the drive shaft be unbalanced? i have no idea what the deal is and could really use some suggestions. thanks guys.