I am no expert but I have a 86 stx.
The fm145 manual trans is known for being weak, be gentle. also I do not like the automatic 4wd system. The automatic hubs have caused me problems until replaced with manual. The bad hubs damaged the transfer case. I don't know if the stock axles and driveling are up to the lift and tires in stock form it is a great truck and has taken me over some very challenging 4wd trips and the truck will run a long time with just routine maintenance.
Regarding you lights, like you said check bulbs, I have had similar problems with broken bulbs. | 
