bluepp....your tc is locked up in third. It only unlocks briefly to make the 3/4 shift and then locks up again so you are able to lock much earlier than 50mph. I also have two customers with the G-56 trans that have installed the gear vendor unit. I know for sure that one is getting better highway mpg number and most of all, doesn't have to sit there and listen to the engine buzz at 2400-2500 rpm. He loves the 6 for towing, but was majorly disappointed in the 75mph cruising empty performance. The gear vendor rectified that. Will it pay for itself? Most likely not, but he's happy.

 

I have a 6 speed with 373 gears and mines at 2000 rpms at 65 and around 2200 at 70mph. if my bobtail truck had a 7th gear that would drop my rpms 450 I would still have no trouble going up any hill in high gear at 70mph at 1750 rpms. you have an AUTOMATIC with a DIFFERENT final drive ratio. I believe the guy who started this post also has 410 gears with an auto trans which would put him closer to my ratio. with your setup my statement doesnt apply but I wasnt talking to you or about your truck. as for our problem "which you do not share" your wrong completely. adding an overdrive will put his truck within 150 rpms of "yours" on the freeway. does your truck get crappy mileage because of its final drive ratio? would 150 less rpm's kill "your" mileage or keep you from being able to climb hills? I dont think so

 

I just drove 2600 round trip and had he cruise set at 75-77 the majority of the trip and averaged 18mpg hand calculated. My truck has about 17k now and my mileage went up with every trip. I am sure it will not get much better. I had my quad box on the 60hp setting.

 

Joe what tranny you got and what were your rpms?

I have g56 6speed 2200rpms at 75mph