I've got a '94 F150 with a 4.9, with just over 140k. Except for a recent problem in which I have gone through 7 alternators, it's been a great truck. For the past several years though, it runs as if it has water in the gas - really lacking power, especially on hills. I've tried all sorts of engine and oil additives, new plugs, wires, fuel filter, PCV - any suggestions would be appreciated.

 

Does it have the single or dual fuel pump set up? If the in tank pump works ok, and you have a problem with the frame mounted pump, it'll still run, not very good though.

Whens the last time you changed the fuel filter? or had the injectors cleaned(through the rail)?
With that many miles, I'm sure your down a little on compression, you could stand to add a few degrees of static timing to it, that will help.
I had an 87 4.9 its still going, the guy I sold it to (2 years ago)just had me do the second(sinces hes had it) tune up. I sold it with 133K for $2200.00, he now has 190K and it sounds great.

 

I had some bad gas the other day but I think it was because I ate Mexican food the night before. When you do get bad gas make sure you share it with other people.