7.3L hard shift ONLY while towing

[Cattflight]

Howdy, all!
I've been towing my 40' fifth wheel with this truck for about 3 years. Shifts are typically a little harder than when not towing. But yesterday, I noticed a REALLY stiff shift from 2nd to 3rd gear upon acceleration. Though I didn't chronicle the exact circumstances, I want to say it shifted at a higher RPM than usual. At the same time, I hear a sort of quick "swoosh" sound but a little metallic. It's hard to describe.

The truck runs perfectly without the load. Shifts and TC lockup all as expected and smooth.Any ideas? This is an '02 with 230k miles and I bought it used at 195k. It's got a Garrett 38 turbo and an Edge Commander. The Edge is set to setting 1 "tow". Again, never had such a hard shifting before.

 

[bcvickers]

I'd check your exhaust back pressure sensor and sensor tube. From what I have read the ECM uses that information as input on fueling and shifting.

When is the last time you did a transmission filter and fluid swap?

 

[kenter55]

What truck is it. We’re in the dark here.

 

[bcvickers]

What truck is it. We’re in the dark here.

It's an '02 with 230k miles on it listed in the 7.3 forum so I'm just going with that...

 

[kenter55]

It's an '02 with 230k miles on it listed in the 7.3 forum so I'm just going with that...

F350, 250, dually,.... ?

 

[01yellerCobra]

Don't forget your foot is usually in it a little more to get moving when you're towing. The computer reads that and ups the pressure in the trans to keep it from slipping. And also if you're pushing the throttle more the ECU is going to wind out the RPM before shifting. Think of the difference between part throttle and WOT shifting.

 

[kenter55]

Also, I’m not sure but I think, that with enough load and throttle the torq conv might not kick out and back in on some shifts like it does on others.

 

[Cattflight]

Hey gang. Was offline traveling for a couple weeks. I had a shop in Vegas put in a TransGo shift kit and a new solenoid pack, and now everything works wonderfully. Valve springs were worn out according to the tech. They also replaced the line boost valve with slightly higher pressure to assist the towing. Good, firm shifts and I don;t feel under-powered pulling uphill. Filters (factory and aux) and fluid levels were fine.

Maybe this was overkill, but not being a diesel motorhead, it all seemed tangible to me.