Q: Engine bogs down going uphill

Considering the age of your vehicle, I would suspect the catalytic converter might be having issues. Catalytic converters are an emission component that are located on your exhaust pipe. Over time, the insides of the converter start to fail and clog up. This prevents the exhaust from escaping. This overheats the converter. This is a vicious circle, since the hotter the converter gets, the more it closes up inside. Letting off the pedal usually lessens the exhaust and helps it cool down enough to run a bit better. A back pressure test can determine if this is in fact the case. The replacement converter will need to be welded on the exhaust pipe. I recommend having this problem inspected by a professional, and having them replace the catalytic converter if necessary.