I'd bet coincidence. Older Toyota V8s (the 4.5 and 4.7) have a timing belt and seem to be trouble free when towing.

Interestingly enough, the 4 cylinder Duramax diesel in the new Colorado/Canyon has a timing belt and a pretty high towing capacity!

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-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.