91 full size blazer...acceleration/hard start

Bought a 91 blazer in feb. 2004. Since I purchased it has been hard starting when hot. Cold it starts beautifully. Replaced the fuel filter o2 sensor is fairly new had the timing adjusted and had quite a few other things checked on the truck. Only to have it continue to hard start. Also when running for over an hour (long drives) the truck loses speed. The engine doesn't whine or anything and the trans seems to shift fine or stay in it's current gear when this happens. Just doesn't seem to want to get out of it's own way no matter how far down the gas pedal is pushed (does this more so on hills than a straight stretch. but has done it on both). Any ideas as to what the problem may be? I've been told so far either fuel pump or computer but most likely computer as it is an intermittent problem not a constant. Was told it runs too rich also. Needs a new cat after just having it replaced about 2 months ago. Any help or advice would be great!!!!! Thanks!