[usnkricket]

I have a 350 Chevy suburban that starts and runs out good but on the highway after running at highway speed, if I take my foot of the gas I get backfiring out the exhaust also I have some trouble with spark plug caps getting hard and brittle. I have not seen any red manifold.
Any help for me or better yet my motor.
Thanks

 

[arch]

carb, FI?