I agree with faulty glow plugs as being the first thing to check. Just remember that they are 5v and if hooked to battery voltage for more than about 4 seconds can overheat and burn up (trust me).
The transmisiion is a Borg-Warner T5 and is very common. Locating another one should be very easy to do. The only difference will be internal gear ratios, as the diesel had lower first and second. I'm using one from a 4cyl gas and it works great. All mid 80's to mid 90 S10/S15 manual transmissions were B-W T5. I wouldn't bother with the old one, just use the bell housing from the diesel and bolt it onto another T5.