Have a '90 K5. Just installed 3" TC front springs and 4" blocks. Now I have 2 vibration problems. 1) At very slow speeds 10-20 mph I get a "shake" (not so much a high frequency vibration). It feels like when you go slow in a truck with VERY aggressive knobby tires. It does this when you accelerate and decelerate. 2) I get a high frequency vibration that is present at higher speeds. The funny thing is that if I take my foot off the accelerator it will stop. Press the gas again and there it is?????? This "vibration" resonates throughout the truck. So far I have changed both U-joints on rear driveshaft, and installed new front brakes (one member told me could be a brake problem). I also have had new tires (only 3,000 miles on them) REbalanced. Nothing has made any change at all. Questions: 1) Could this be a driveline angle problem? If so, should I just have a longer driveshaft made? 2) I was told yesterday to shim the rear end with angled shims to rotate it so it's facing up towards the transfer case which would reduce the angles. However, I have never seen any shims like this. Would this work, and if so where do I buy them? Also, I would rather not go the route of dropping the transfer case. 3) Since this problem seems to stop when I take my foot off the gas does that eliminate a driveline angle problem seeing as how everything is still turning even though I'm essentially coasting? 4) This truck has 256,000 miles on original engine and tranny. I don't want to overlook the fact that it could be something engine or tranny related. Could this be it??? 5) Some have said it could be axle wrap. I am not really familiar with what this feels like but it seems from what I have heard the this is present during hard acceleration. Am I correct on this? If so I just don't think this is my problem considering what I've stated above. The "shaking" is present during acceleration AND deceleration, and it does it during very slow acceleration. I have tried to be as descriptive as possible. If I need to provide any other information please let me know. I am ready to get my truck RIGHT. I can't stand it when something is wrong with it. It is NO fun to drive right now. Thanks in advance for the help.