1990 4runner tranny troubles

Ive had my 1990 4unner (V6, 4wd, auto-tran) for 2 years and have noticed some problems creeping up. First and foremost im having a severe transmission issue preventing me from shifting into 4th gear and overdrive. I have to drive the vehicle for quite some time (at least an hour) before it is warm enough to shift into 4th gear immediately followed by a shift into overdrive. This is quite annoying as 65mph on the freeway translates to 3100rpm or so and terrible gas milage. Often once it actually shifts ill be cruising along and out of nowhere it jumps down to 3rd gear again, often on a long downhill stretch where i let off the gas. Also, taking sharp left (sometimes right?) corners produces a loud creaking noise. The truck handles beautifully, has no vacuum leaks, generally a great vehicle and one I would like to hang on to. Any advice is more than welcome! (btw it has over 244,000 miles on original engine and transmission, both seem to be in great condition)

Change thermostat and it will warm engine up within 5 minutes or so and shift into overdrive and lock up quicker again as before...might treat it to a transmission fluid and filter change if it hasn't been done in last 50,000 miles.....

On squeek/creaking noise...I would rock it side to side to see if I could reproduce it and dial in on what it is that way...often it is body mount bushing,swaybar bushings,shock bushings,rack mount bushings,A-frame bushings ect.ect.ect. that cause that sound...if you can't track it down and it does it consistently a certain place or way you drive...I would mix up 3 parts water to 1 part liquid dish soap and squirt it on a few different bushings at a time and see if it stops making noise....from there you can tight,replace or just give it another squirt now and again....goodluck lol

Having to downshift taking hills is normal and most noticable when in cruise.Change thermostat and it will warm engine up within 5 minutes or so and shift into overdrive and lock up quicker again as before...might treat it to a transmission fluid and filter change if it hasn't been done in last 50,000 miles.....

On squeek/creaking noise...I would rock it side to side to see if I could reproduce it and dial in on what it is that way...often it is body mount bushing,swaybar bushings,shock bushings,rack mount bushings,A-frame bushings ect.ect.ect. that cause that sound...if you can't track it down and it does it consistently a certain place or way you drive...I would mix up 3 parts water to 1 part liquid dish soap and squirt it on a few different bushings at a time and see if it stops making noise....from there you can tight,replace or just give it another squirt now and again....goodluck lol

Well i must say thankyou so VERY much for the thermostat advice, i had a local dealership replace the thermostat (other... people... touching my baby, it was scary) and i decided to take the freeway home just so i could open up. Low and behold the damn thing flew into overdrive like it was new. No more 3100rpm drives home! No more crappy gas milage! Thankyou so much! That was about the cheapest repair i can remember ($30 parts - not just thermostate, $70 labor eek!) Anyway there is a point to all this. On your advice i tried rocking the vehicle, jumping on it, pushing it as hard as i could, hell i even kicked it a couple times. I heard some normal sounding squeeks but not the CREEAAK i hear when i take sharp corners. I will take your advice, having used the same 2/3 water 1/3 soap approach to fix my vacuum leaks in the past, hopefully ill find the culprit. However i might just get apathetic now that my major problem is solved :) Thanks again!

Oh whata feeling...you're welcome lol