i recently got a 93 ES300, what would make it have this problem,

When you turn it on the speedometer reads 80MPH and 1500RPM, even when it is in park, once it is in gear the gauges go back to normal but it stays in 3rd gear, i thought it might be something wrong with the transmission being as that it stays in 3rd gear when driving, you can drive it perfect if you shift manually, but once changed the transmission it still has the same problem, i believe now it is the computer but dont want to buy that and it not be the problem, what is your suggestion on what the problem could be?

 

I'd check to see that there isnt any corrosion on the ground side of the cluster. Pull trim and the cluster out and check it with a known good custer is a great way to check and see what to do. A trip to the junkyard helps. That way if it isnt the cluster you didnt pay a lot for it. The speed is from the abs rings on the axles so you can check the wiring from there to the ECM. An ECM is easy to get to if you go to the junkyard. You can get both the cluster and ECM and not drop more than 100 dollars for both.