Towing with 68 RFE Transmission

[Jim W]

My truck has never hunted for gears that I could tell. But the engine RPM's when doing 55 MPH up I70 behind the semis when pulling my Cedar Creek. They would drop below 1500RPM's in 6th gear, the EGT's would rise above 1100F, and boost pressure would fall off. The trans temps in the sump would raise to around 210 if my memory service me correctly. That is when I would lock out 6th gear, to get the engine RPM's up around 2,000 in 5th gear the EGT's would fall below 1,000F and the trans temps would slowly come down to 200 or so.

 

[Ozymandias]

My truck has never hunted for gears that I could tell. But the engine RPM's when doing 55 MPH up I70 behind the semis when pulling my Cedar Creek. They would drop below 1500RPM's in 6th gear, the EGT's would rise above 1100F, and boost pressure would fall off. The trans temps in the sump would raise to around 210 if my memory service me correctly. That is when I would lock out 6th gear, to get the engine RPM's up around 2,000 in 5th gear the EGT's would fall below 1,000F and the trans temps would slowly come down to 200 or so.

Yeah, I'd do the same in this situation.
I think the newer ones will downshift in this situation by themselves as it is lugging the engine.

Raising Trans temps is always an indication for an open TC clutch, in your case probably open in 6th but locked in 5th.
My old four speed acts similar under the same circumstances.