[nubiecanobie]

I have a C6 with 3.54 final drive. The stock tires are 235/85R16. Are there bigger tires that I can put on the stock steel rims to increase hwy fuel economy? What are the pros and cons? TIA

 

[Mr_Roboto]

Those are the tallest tires that will fit in the wheelwells. Stock tires on the vans (at least mine) are 245/75R16, so the 235/85's are taller than the stock tires.

Your least expensive option is to swap in a rear axle with a higher (numerically lower) ratio. Although I'm not sure if you will find stock gears higher than 3.54 in a 1 ton axle. I've seen 2.79 and 3.00 axles in Fords, but those were 1/2 tons.