With the smaller cam you might see 30-40hp gains at the max. The heads are what kill the performance and were designed with strict bottom end torque. To get another 20-30hp you need to junk the stock heads and get some EQ heads. If you had a 96+ truck I would highly recommend fixing the plenum gasket, if it hasn't been done yet, 52mm TB and a set of headers along with a tune and you wouldn't even need to worry about the cam or heads. If the plenum hasn't been fixed already there will be some mpg increases with that and maybe a slight touch of power if you are pinging. Being that it is a OBD1 I wouldn't change the cam unless you go with an RV cam. The computer will learn a bigger cam but not to the full degree. Some bolt-ons will do you fine.