Accord - Up Slope

Hi all, My car (1990 Honda Accord, Auto, 142K, 4 cyl) runs good otherwise. Only when going up slope, it is kind of slow.. doesnt go more than around 30mph. It feels kind of uncomfortable when going up slope. Can anybody please tell me what could be the reason ? And is there anything that I could do to improve on this? I know that it is a pretty old car and it has its own limitations, but any suggestions would be appreciated, especially since I am soon going to spend some $$ on replacing its time-belt. Thanks in advance! QGoogle