Toyota Pickup

I have a 1998 Toyota Tacoma 2wd 2.4 eng. When I first bought it I notice a rough idle. And at cruising speeds, the engine would buck. I gave it a tune-up ( plugs, wires, pcv valve, air filter). I didn't get to the fuel filter yet. The air filter was so clogged, that the mat sensor got dirtty also. I also replaced the o2 sensors. After replcaing all of this plus cleaning the mat sensor, the truck ran great. A full tank latter, it started to do the same thing. The check engine light never came on. PLEASE HELP!
April 30, 2006.

How much is too much fuel. That truck should get about 20 in town and about 26 on the road. I know I have one. CHANGE the fuel filter for sure. It is a real pain because it is under the intake manifold. Also check you fuel pressure regulator. Did you clean the MAS? Let me know

May 1, 2006.
I replaced the fuel filter, egr valve, and throtle position switch. I cleaned the mas sensor. The problem went away. It does'nt buck st high speeds any more, and mileage has increased. Within 5,000 mi, I've seemed to lose power and idles rough again, only when it warms up. My gas consuption has increased to 17-20 mpg, but I should be getting above 25 mpg. Once in a while I'll hear a hissing sound from the tailpipe. Can you help me?

Aug 25, 2006.