I have a '98 4wd Navigator. 115K on it, I have had it since 2000 & 40K were on it then. Normal maintainance, 3" magnaflow system, 22's and that is it. In the last 6 - 8 months it really feels down on power. Some of it may be due to I only drive in on Saturdays so it only feels doggy. The rest of the time I drive my car, an '01 LS V8 Sport. But still it is seeming weaker. Disassembled and cleaned the TB, have run injector cleaner, new fuel filter, air cleaner, plugs @ 101K. Just seems down, runs smooth, starts easy, still gets 10 - 12 in town.
Any suggestions? Pressure cleaning the fuel injectors maybe?

i have a 2000 and sometimes it seems she is low on power, but lately i've been only running 89 octane from shell. its usually 93, but gas is hell. when i do use the lower octane i fill it up and get some octane booster and dump it in after i fill up. seems to pep her back up. i too did all the maintenance stuff alittle over a month ago and still feels a little sluggish maybe a blower is in order. i get around 113-15 around town and 17-18 on highway if i run at 67mph.