i have a 91 runner, v6 auto tranny. when i hit 4th before i was able to maintain 70 mph at a fairly low rpm. now all of a sudden when i hit 4th, it drops about 400-500 rpms less! it barely even helps now. ive done all kinds of searches with no success. any ideas?

 

Sounds like your torque converter ain't locking up. Good enough for a guess?

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Change the thermostat.