1991 pickup troubles. Ideas??

I recently got a '91 pickup with 208,000 miles. Couple days ago, driving @70mph on hiway the truck lost ability to maintain speed from 70 to @55-60 depending on hills -- no loud noise, minor 'stutter' of the truck, or any other significant occurance. Also, the fuel gauge went from 3/4 to 1/2 tank in seconds. The truck idle is a bit rougher now, exhaust sounds louder (and is in bad shape), but otherwise, it starts up, runs, and drives okay - just with no higher rpm accelleration throughout the gears. Not sure if its fuel filter/pumps, exhaust issues, or, transmission or engine issues. Any ideas anyone? Any insight would be very helpful and appreciated. Thanks.

Clogged fuel filter and/or clogged cat conv (especially considering the mileage and if it's the original cat).

The hill thing really says clogged cat conv.

Clogged fuel filter and/or clogged cat conv (especially considering the mileage and if it's the original cat).

The hill thing really says clogged cat conv.

X2

Marsal