Beyond the obvious of it not being anywhere near the ideal gear set, would 3.21s w/ a 3.6 and 35s be worse, better, or the same as my 4.10s w/ 3.8 and 34s.

On the chart, they both fall at the bottom but I ran my 34s in my 07 for 90k miles with no complaints.

 

according to the chart, there doesnt seem to be much of a difference. ive been running 3.21 gears and 35's for roughly 10k miles since i moved back here to Pittsburgh. the 3.21's arent all that bad, but nowhere great either. i get roughly 15-16 mpg on highway but despite all the negative comments on the forum from other members i didnt really think they were all that bad but i just ordered yukon 4.56 gears to install in the next week or so.

 

You'd probably get better mileage with 3.73s or 4.10s with the new engine and 35s.

 

Would be much better as the 3.6 has a lot more power than the 3.8. The new tranny will also make it better.