1996 Tourmaster lurching issue
I've got the oddest issue hopefully I can properly explain it. 3 years ago when I first bought the RV I noticed that the cruise control didn't work well. When I'd set the speed the rig would start to jump gears back and forth between 5 and 6. So I didn't use it again for a year or so and then tried again but thought perhaps the engine brake being on didn't jive well with the cruise control so I turned it off and it worked great.
Suddenly a few days ago 2000 miles into a cross country drive the issue returned. I started flipping the engine brake on and off, the cruise main switch off and on and after some combo it seemed to work again. This happened a couple more times and flipping switches always seemed to "reset" it.
Today the issue returned and wouldn't stop so I drove without cruise but then I started to get random lurches. At first I thought it was dropping into 5th or 4th but it happened so quickly I couldn't look at the Allison gear selector, but I could see the RPMs actually dropping when the lurches happened.
So I'm wondering if something in my engine braking system is malfunctioning I think I have an exhaust brake as I can't hear the stereotypical big rig rat a tat tat you get with a jake brake. Where is the valve located on the exhaust? Can I disable it to test my theory?
Cummins M11 400HP engine and Allison transmission