Good question. One I don't have an answer for. However, the diesel uses the 48R? trans, so, that may explain some of it.

For the adjustment, I go by what MonteC recommends. He runs a trans shop somewhere on the eastern seaboard of the US, and has been doing these for quite some time.

 

I thought some diesels used the 47re transmission?
I will follow the advice of experience.

 

The FSM also mentions points to measure pressure at.

 

That's for diagnosing shifting issues.

 

Is shifting back and forth between third and forth a shifting issue? Pressure, or PCM? If you have a pressure leak the information fed to the pcm may cause hunting.
Mechanical (seals,valves) and electro mechanical (solenoid, pressure sensors) fail before electronic.
I've been using DEOXIT to clean up the green death on contact points (a mechanical connection) in older vehicles. Pricey, but it seems to work.
Blast it first with brake clean, then air and a drib of Deoxit. A guy who repairs tube amps told me about it.

 

How much of an RPM drop are you seeing?

 

I bought a used Snap On scanner with all the extras on Ebay.

 

Good plan. I think the MT2500 will work up to the 2006 model year, solus, or newer, will go even further.

 

On mine that spring busted. A common problem.It had issues shifting 2nd to 3rd.
an overdrive.
I replaced the spring,sensors an overdrive an adjusted bands..Runs fine now

 

I believe you have the wrong location of the accumulator spring marked.