02 Static Noma Noise

I static dropped my 02 Noma with ZQ8 with 2" spindles in the front and 3" blocks with air shocks in the back.  Every time I ride with it with the back down lower than the front I get a knocking noise that speeds up as I pick up speed.  It seems to only be in first gear, and I can baby it to second and it will be fine unless it downshifts.  The only thing I can think of is my drive shaft is going too far into the tranny and causing the noise, and needs to be shortened.  Its an extended cab so it has the 3 piece drive shaft on it.  What does everyone think?  If it does need to be shortened is there a magic measurement that I should go with because bags are definitely in my future.  It needs to be short enough to stop the noise and save me from replacing U Bolts, but long enough not to fall out of the tranny once I bag it.  

well i had the same problem with my oo extended cab noma and mine was the rear u-joint. but everytime i replaced it, it would go out again in time. but i was told i could put a 1 piece drive shaft in place of the 3 piece. but the truck got reposessed so i never tried it.