197000 miles never replaced,engines runs rough

It has a V6. The alternator belt was bad so I thought I'd change all the belts at the same time. Maybe someone can give some advice on how to get that pesky ac belt on? Thanks for any advice!

3.0 Liter

run at normal speeds it will stays cool just in the center of the gauge. stop and turn it off let it sit for a few mins. and restart and if will get hot drive down the road or sit and rev it up and will cool down. Coolant level is good fan is good fan clutch good and no leaks from the water pump. It will fill up the over flow and loss of some coolant so I think water pump is working. could it be the thermostat sticking? will not overheat after I get it to cool down. also the radiator was replaced 2 years ago. thanks for your help

Recently overheated oil looks ok what do i do and how much will it cost?

Automatic. After sitting awhile it will go back into 4 high by itself. Thanks

Tried to perform a code retrieval on my 94 4runner. Check engine light did not illuminate with jumper wire, so tried without wire and still no light. Just out of curiosity I pulled the ECM fuse under the dash and turned over the engine, which started. So my question is can it still run with a bad ECM? It would appear so to me but need help.

automatic fluid is leaking into transfer case come out vent on top of transfer case how to change seal and now it does not go at all no fluid I am guessing

It starts to miss and jurk

I change valve cover and intake gaskets. now she will not stay running. starts for just a few seconds, no issues before that. I have made sure I didn't cross or leave off a vacuum line checked each over ten or more times. I narrowed it down to the injectors or not firing. power to both wirers. had the ecm checked was good, even swapped it out with one that was in a running 4run. fuel pump is working. don't know where to go from here. everybody I have tried to get help from is stumped as will. no codes also