I have the 3.7 in my T and get around 14 in town. I have gotten 19-21 multiple times on the highway driving 65. I think the aerodynamics of the snugtop make a difference though.

 

v8 getting 21 ANYTIME??? and i max at 17.2in my h307 3.7

the 3.5 is specked a little higher i think and the 3.7 hp is rated at about 4000 rpm and the 3.5 much lower rpm.
i dont really see any benefit to 3.7
i dont spend much time at 4000 rpm.
i drove my friends 06 3.5 and see no difference, ill take the mileage,
and if the 5.3 EVER hits 21 then thats the buy!! for me as i think of one last new vehicle.
tom

 

07 H3 with Adventure Package and aftermarket wheels (1.5" "stick-out") 17.6/Hwy 16/Town - If at the time of my purchase I could have bought an Alpha for 4,000 more than the I5 I would have bought it -the price differential was almost $15,000 between Alpha and no lux adventure package.

 

yesterday was the first time I checked mileage on my 09 c/e v8 and got 17 mpg with 18" wheels and magnaflow exhaust.

Frankly I don't concern myself with trying to "milk" the best mileage out of it.

 

Check your tire pressure. If it is too low, add air to bring tires to their recommended pressure. Check your air filter. If it is dirty or old, replace it.

 

there are hundreds of other posts asking the same question if you take a minute to look around. you will average about 16-17mpg. with best condition, and i mean absolute best you will have is 20mpg. for about 3 seconds before it drops to 19 again.

youl wouldnt get 24mpg with the engine off and car in neutral going down a hill, as the other gentleman mentioned. that is a big load of cow poo.

 

^Since I had posted this thread, I have taken quite a bit of time searching (the search really isn't great but I'm finding more posts), and I've found 18 on the highway with the 5 cylinder seems to be fairly common. Perhaps a mileage sticky needs to be added, as there is certainly a lot people who want to know not only what other owners are getting, but ways to improve their own mileage.