I recently installed a 4inch lift onto my blazer an shortly after that i had to extend my rear driveshaft b/c it broke one of my u-joints. Then I installed the new driveshaft with new u-joints and it drove fine for about a month.

The problem that i have is that when it tries to shift from 1st to 2nd gear there is a loud grinding noise coming from my drive line somewhere but i'm unable to find out what the problem is. I checked all fluids and they were good.

Any help would be appreciated. Thanks

You lengthened you drive shaft, but did you do anything about the angle at which your driveshaft is running at. Take your U-jionts apart, and I'll bet you find the needle bearings turning to powder. 4" is alot of lift, they make wedges that go between your axle and your rear springs to bring your driveline angle back to were it should be.