1995 GMC K1500 350TBI 168k miles. Problem started a year ago. The truck idles fine sometimes, then starts to idle rough then dies. It does not do this all of the time. On the freeway (constant speeds of 55 and above) the truck will drive fine then the RPM's will drop (engine loses power). I have to give it more gas to stay at speed. If it is on cruise control, the trans downshifts and revs the motor up, then upshifts to continue cruise speed. Previous owner replaced the fuel pump and screen (mechanic did not clean tank) and fuel filter. I changed the plugs, wires, cap and rotor, PCV valve and fuel filter in the summer. Still no help. I changed the fuel filter and drop'd the tank today, wiped down where I could in the center baffle of the tank, and installed a new screen. I will put the tank on in the morning. I think its a fuel problem but it may be a vac leak also. The trans shifts fine and the trans would not cause the bad idle anyways. Any suggestions of what I should check out?