won't downshift while on cruise
 

Hello I have a 1999 Ram 1500, SB, Reg cab, 5.2L, auto, 68,000 miles, K&N cold air intake, cat back magnaflow.
When on cruise at 65 or whatever speed it wont downshift till 45 or so. Without cruise or when helping the cruise with the accelarator it downshifts normally.
Any ideas?

RE: won't downshift while on cruise
 

OK. Did a search and found some possible answers. Probably vacume related since my AC vents shift under load. Will replace the check valves in the vacume lines and the PVC valve. The servo line under the battery looks fine as do all the lines. Can't hear any hissing either.

Someone once told me that I could spray carb cleaner or WD40 on the lines and fittings with the engine running and I would hear the change in RPM. Has anyone heard this? Would it dammage the lines?

Thanks