Brown T

I seek help with an ongoing problem.
When I start my journey my truck goes through the gears to what I call 4th gear but fail to go into overdrive so the rev meter is at 2000 rpm or higher, the speedometer about 40-50 mph for at least 5 miles.
If I stop the car turn everything off for about 30 sec then restart my journey it goes through all the gears including what I call overdrive now the vehicle feels treat the rev meter now at about 1200 - 1500 rpm and the speedometer about 50 to 60 mph this work for a while maybe 8miles then you feel the gear shift down (decelerates) verry annoying. I have had several mechanics worked on this problem but no joy ..Can anyone advise me on how to resolve this problem?. I am now retired so I intend to try and fix it myself operative word here is try.
As I understand it my engin diagnostic connector is odb1, is there an adaptor I can use to convert to odb2 which is now the standard that I can use for trouble shooting the engin performance etc?
Your assistance would be greatly appreciated.
Thanks

cbr600rx7

Could be a number of issues causing this and it's not just a Toyota specific problem. I have seen 45/545RFEs do the same thing.

Any way can you give us some history and more details about the vehicle?
Year, motor, miles, etc
Have you changed the fluid or filter recently?

Brown T

Thanks for your prompt response.
1995 4Runnern, Engin is 3vze, Milage 178956. California model.
The engin has been serviced several time ie plugs, all filters replaced and tune up. Transmission services 2years ago, the head gaskets have been changed 6 months ago yet the problem exist. The computed have been changed in The past.
Hope this help.