1990 toyota-not much power

I have a 1990 toyota x-cab 4X4 with 190,000 miles,the top end of the engine rebuilt with only 30,000.If you come to a hill on the expressway the only way to maintain speed is to kick in the passing gear.it doesnt seem to have a miss,but only gets about 11M.p.g. on the highway.I realize these

3.0 engines arent powerhouses,but i feel something must be wrong.I have only owned the truck 2 weeks,so Im not real familiar with it yet. Any advise would be helpful.