5R55E Slipping.

[UgLeeXLT]

1998 4.0 pushrod with 5R55E Trans. 300k miles.
Drives with manual selection in 1 and 2.
No positive drive in D or R.
Selecting D or R causes a 'takeup' clunk but then after an initial very slow movement there's no drive.
Using 1 + 2 to get up to speed and selecting D will allow Overdrive to make cruising possible. 3rd(?) 4th(?) still slips but will allow O selection.

I'm assuming it's a Valve Body Gasket issue but all the forum links for information on it are 'dead'.
Searches on the internet as a whole have been disappointing.
Am I correct in my assumptions and if so where would be the suggested place for the best info?

Many thanks, Ug

 

[JK080]

Blown out valve body gaskets can cause all kinds of issues, the symptoms can vary depending on where the gasket has failed and what hydraulic circuits are affected.

Not having drive or reverse but able to engage manual low and 2nd and able to shift up through the gears once up to speed is a classic symptom for a failed input sprag. This sprag is located in the overdrive section of the transmission and would require the removal and disassembly of the transmission, at this point it should be just rebuilt.

 

[UgLeeXLT]

Blown out valve body gaskets can cause all kinds of issues, the symptoms can vary depending on where the gasket has failed and what hydraulic circuits are affected.

Not having drive or reverse but able to engage manual low and 2nd and able to shift up through the gears once up to speed is a classic symptom for a failed input sprag. This sprag is located in the overdrive section of the transmission and would require the removal and disassembly of the transmission, at this point it should be just rebuilt.

Thank you JK. With more time yesterday evening I looked at more threads and saw the sprag mentioned. I'm a Manual transmission person so this is all new to me.