94 Itasca w/Chevy 454- Backfire issue!!!

[christoph]

We have had our Itasca for just a year now. Got it used last spring.
had 43000. miles and well kept and maintained, have all the records.
This spring after running a tank of gas through on our first trip. Noticed
on small inclines like one would encounter on the interstates of
Michigan and Indiana, when the tranny would downshift the engine
would backfire every now and then. Any ideas on what causes
the engine to backfire when loaded and out of overdrive (passing
or normal drive) running 2500 to 3000 rpm's. The engine normally
runs 2000 rpm at 60 mph in overdrive. Also noticed a strong shudder when at
a steady speed between 40 and 55 mph. add just a little gas and its gone??

[bigskymt]

I would ohm out the plug wires first.

[SteveLevin]

Exhaust leaks are the typical source of backfires. They can be pretty small and still make a lot of noise.

Steve