Just take your time and logically figure out what it could be. It is probably something you didn't quite get back together right.
I have a lot of experience in figuring out problems on a lot of diffeerent types of machines and there is one common problem with the way most people do it. They start changing things before they find the root of the problem. In doing this they usually do not fix the problem correctly and they often create other problems.
If it is one thing that I have learned it is that if it doesn't make sense it probably is not correct.
'99 GMC K3500 6.5TD Crew Cab dually now SRW, Auto, now 5spd Yeah no more sissy slushbox
3.73 gears, 235/65 tires
Pull about 80% of time, mostly 4K lb hilo type camper