1990 Toyota 4 Runner shifting into 4th too soon

I have a 1990 4x4 Toyota 4 Runner w/automatic transmission . It has a problem with upshifting too soon into 4th gear. It will shift directly from 1st to 4th, 2nd to 4th and so on. It is intermittent, some days not doing it at all, other days, I can drive for 10 - 20 miles before it acts up and yet other times it starts right out of the driveway mis-shifting.

I bought the truck in August 2005 knowing it had the problem but at a fairly good price considering its overall good condition. I thought that it would be an easy to remedy electrical or sensor issue.

However, the first transmission shop insisted on a rebuild of the tranny. After the rebuild it still had the problem. Further investigation found some frayed and broken wires. A couple of shops have looked at it but all they find is more bad wires and they all give

up, although, we believe all the wires are now repaired but it still has the problem.

I called the previous owner only to find out he "forgot" to mention a friend of his changed out the tranny for him about a year before in his

personal garage with a used transmisiion (not a rebuild). He also changed out the ECM computer. One garage suspects a major mismatch as we have also found transmission wiring colors don't match the computer wiring harness.

Anyone have any suggestions? One shop mentioned a dealer reflashing the computer.

Reply to
clarkrs
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