Chevy & GMC Vans

I want to change my 90 provan tiger to awd I have a 93 donar, what am I getting myself into??

Easy Peasy.
just Swap Subframes from a 2wd to an awd frame.
Easier still if you have the awd frame already set up with an engine and transmission ready to go in.
2wd trans will need to swapped for an AWD trans of course and a T-Case will be nedded as well.
Best to just get all that from the van that donates the awd frame.
I did it to my 87 van. check out my "DoYouLikeItHere's Harem" thread...
viewtopic.php?f=16&t=6380

what about the computer does it have to be changed?? or modified

if it is a 1990, it has a 2wd 700r4.
use a 4wd 700r4 (90-94) year it should be no prob.
Dont try to use a 4l60E in place of a 700R4 and vice versa.
Got pix of your Tiger?
Rule 6B ya'know..