After over two years of no problems with my 2002 PF SE (55K miles), I
have started experiencing a problem when I'm at speeds of 70-75 mph
and there is any sort of incline that puts the engine under load.  It
almost feels as if the engine is missing or hesitating and there is no
acceleration power when I push on the gas.  I thought it could be the
air filter so I changed the air filter.  No better so I brought it
into the dealer and the computer check showed no problem (or codes).
Even had the mechanic take a ride with the computer hooked up to
recreate the problem and although he could feel it, nothing showed up
on the computer.  He suggested that the fuel filter be replaced and
that we run some hi concentrate injector cleaner (formula 44 or
something no available to consumers) thru one tank of gas.  Although
the engine ran better overall after that, the problem remained.  He
suggested that there might be problems beginning with the spark plugs
so I had the plugs replaced (a little expensive) but that has not
cleared up the problem.

Any thoughts on what it could be?  The mechanic is basically
approaching this on a "rule out one thing at a time basis".  What else
could be causing this problem?  WHile it seems like it is fuel
related, I want to consider everything.  While I can't make any
connection to it, the problems started somewhat around my last oil
change at JiffyLube.  Anything they could have done?  I've checked for
hoses or wires disconnected.  Could this be at all related to bad
tires or an alignment problem?  I'm pulling at straws here but don't
really want to rule out anything since I have no good ideas at the
moment.  Other than this problem, the PF runs great and has good
pickup and power most of the rest of the time.  IDels like a
champ...hardly know it's on.

Any help appreciated..