On 3rd transmission3rd and overdrive keep blowing out

I would try changing the whole fuse panel, try a junk yard to save money

if it doesnt switch you may have a vaccum leak, but i work for a junk yard and we seel alot of heater controls for this car you may want to get a new or used one from a junk yard

Usually the transmission needs to be rebuilt in that situation. It's a very common problem if that's the famous automatic overdrive transmsission. AOD I have had three trucks that have done that. It usually starts by shuttering when it shifts and than finally goes out. Sometimes the Lucas transmission treatment gives you a little more time, but it sounds too late for yours. From what I understand (mechanic told me) that when the overdrive goes out, it takes third gear with it. If you drive in hilly areas, that overdrive is shifting in and out all the time as you go up and down hills and wears it out. My Dad had that hapen on his F150 and he replaced his transmission with a junk yard transmission that turned out to have the same problem. I had that transmission replaced with a Jasper rebuilt and it worked great. I think it was $1300 for the rebuilt trans with the old one core trade in. I think when 3rd gear goes out, you can only go about 45mph without over reving the engine. I saw that same problem with a Ford Crown vic with that same transmission and 302 engine that my neighbor had.
Did your third gear just go out all of a sudden or were you getting like a shuttering or kind of a grinding sound when it shifted?

these are great transmission,,
just make sure to save up that 30.00 in case the trans range sensor starts going out,,it'll start hunting between 2nd and 3rd or overdrive and 3rd. thats when ppl think the trannys goin out and dont do anything about it until its too late. have a spare if ya want one. they're 650.00 guaranteed at any salvage yard 90 days. plus core..good luck.

the fact that after you changed the part from the junk yard it blew warm air indicates that the heater core is not the problem
could be the heater control is not fully opening or the junk yard replacement part is faulty

sounds like its internal, like the reverse band, that applies the overdrive, or the clutches that apply when in overdrive, either way the reverse band and overdrive clutches work hand in hand, for overdrive and reverse... id say you need a rebuild or a junk yard unit.... :( sorry for the bad news.

no man sorry but your trans went out it should be a 4l60E trans with overdrive there not too bad if you go to the junk yard

You might try to add a transmission cooler. If its getting hot it will eat the transmission easily. time to swap it out and sell the problem to someone else.

time to consider a visit to the junk yard and fit a manual

im affraid so last resort put a tick aditif in the trany dont expect miracle thank you pierre