i had the same problem my truck has 31K on it and Randy from daves diesel in muncie,in said that my lift pump is starting to go out so he said to get a new lift pump for it. i pull a 11,656 gvw
fifth wheel when i got my truck which is a 2500 24v 5spd 4x4 lwb
i towed the trailer the second day got . so do a pressure check on your lift pump.
vince harris
member of the GLTDR
99 2500 24V isb 5spd 4x4 slt lwb 4. 10 lsd 20,500 gvw 5er pullrite hitch SILENCER RING REMOVED cummins mud flaps autometer pyro and boost gauge's BD exhaust brake K&N air filter
99 35 foot dutchmen 11,656 gvw with slideout