85K miles overdue for a tune up could definitely be a contributing factor.
The t-belt should be done every 120K as well. It's a non-interference engine, but a sloppy old belt won't help it either.
A whole lot of things could be at fault though. Does it ever throw a check engine light? You'll need a Ford-specific code reader, but they are only around $30 at any parts store. You probably have some sort of dummy OBD connector on the dash, but your actual connector is under the hood near the fuse box on a '95. You can use a jumper wire to get the computer to flash the OBD codes with the CEL, but $30 for a digital read out scan tool that comes with a book of all the codes isn't a bad deal IMO.
What's the general maintenance history? Do you know when the fuel filter was last replaced? If you don't, I'd replace the fuel filter before even touching the plugs and wires. A basic "Pro Select" or whatever fuel filter is less than $10 for these trucks and is easy to replace.