I don't think replacing the computer will help any. To replace it, remove the ground from the battery and wait for 15-30 minutes. Then pull out the ECU and replace it with the other. Quite simple.

The 'incorrect' gear ratio is just a note that the engine speed and the tranny are slightly out of synch. This happens when the shift point in the tranny computer is different then the engine shift point. It sometimes happens when over revving or spirited driving.

You just replaced the PNP switch. I would suspect that it is not positioned correctly. Do the backup lights turn on when in reverse? Just turn the key to posII and put it in R and take a look. If not, the PNP needs to be re-aligned.

Re-check the tranny fluid level. When 'hot' it must be at or slightly above the full mark on the hot side of the dipstick. Cold readings can be misleading.

Don't drive the car a lot when in limp mode, too much slipping could damage the converter. You can always try shifting to L and 3 to see if that helps. Cruising in 3rd gear won't hurt, just your gas mileage, and the lockup will not happen for the torque converter.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)