I had almost the same power issues with my 91 with only 92K miles after the PO had his father in law change the timing belt. It was one tooth off on the cam pulley, and that was enough to make the truck impossible to time correctly. Not sure about the oil burning and how it would be connected, but mine needed new valve seals, maybe yours does too. Mitsubishi engines are kind of infamous for the weak OEM valve seals. Actually a lot of 90s vintage Japanese 4 cylinders are.