4L80E hydramatic transmission hates hills

Here’s my take on the problem: from what you have told me (thanks for all of the detail, it helped), your transmission could have any number of problems. Yes I know this looks like a cop-out, but it isn’t. Look at the list of possible problems:

• Torque converter — pump, turbine and stator
• Clutches/bands — without them your motorhome won’t move
• Planetary gears — needed to enable the right gear selection for driving conditions
• Hydraulic system/valve body — ensures the fluid gets to the right gear at the right time
• Input shaft/output shaft — as the names imply they take power and deliver power to the drivetrain
• Electronic systems — since the 1990s, computers have replaced many mechanical actuators and systems because they are faster and more accurate; this includes the sensors such as the throttle position sensor(TPS); the mass airflow sensor (MAF); manifold absolute air pressure sensor (MAP), and the like
• Computerized systems — yes, there is overlap with the last topic but there is a subtle difference and it is that the number of “control modules” (computers) such as the transmission control module (TCM), engine control module (ECM) and the like that may either operate directly in the computer or touch it in some way. By the age of your motorhome there were likely eight computers systems that either dealt directly with the computer or touched it in some way

This is only a partial list of where there may be problems. Yes, you could try with the throttle positioning sensor, but, then you would have to start dealing with the other sensors such as the MAF and the MAP and solenoids, as well as the other control circuits themselves. And, then there are the control modules involved. Which ones might be bad?

What I am saying to you is that I would advise you to take the motorhome into the dealership and let them work on the transmission. Be prepared for some sticker shock, though, because you will likely be spending the better part of $4,000 to make sure the job is done correctly. The good thing about this investment, though, is that you will have a warranty available after the work is done so that if there are other transmission problems, you are covered.

Oh, and my thinking on the problem you described began when the former owner overfilled the transmission by two quarts. The pressures that build up in the transmission and the added pressure exerted by the extra two quarts likely caused many of the problems you motorhome is facing. For example, the blades on the turbine are rather delicate and they could easily have been damaged. The same is true of the checkvalves in the valve body and so on.

Let me know what happens, if you would. I am interested.