a few things to note to see if you have changed it recently
your:
fuel filter (every 50k)
PCV valve (a biggie for gas milelage and only $3)
spark plug gap
spark plugs themselves
spark wires
distributor (clean? not worn out?)
brakes draggin?
compression?
alignment
BG is good for fuel injector cleaner, i never felt a diff with the STP stuff. also a thought, not a suggestion but that stuff you run in your motor before an oil change? and then change your oil haven't had an experience with it but i kno its out there
check all those and see if you have any more problems
for the PCV valve (positive crankcase ventilation valve) its easy to tell if its broken or not... take it off... and shake it.. i fyou can hear something moving.. its good, if u don't... its bad.