Transmission has overdrive. There is a button on the dash to turn it off.
How slow are we talking about? Speed limit is 55 for towing in California. I assume it will do at least that on the flats. What am I looking at In the mountains I don't want to going 15 or 20 up a grade.
I appreciate your concern about the hitch. If i can't find a good one I may buy new. Think about it this way though if you bought a used truck would you imeadlatly replace the hitch on it? If not how is that different than buying a used hitch? I would make sure to use all new grade 8 hardware.
Ok that should be an e4od.
3:55 is definitely not going to be a towing monster. Flat land 55 shouldn't be an issue but it's going to take a while to get going and it will probably bog down considerably on a grade. My 04 F150 with a 5.4 had 3:73's (I think) and it would drop a lot going up mild grades with just a 18' car hauler and a mid size sedan.
And no I wouldn't just change out a hitch on a used truck. But at least I could see what condition the truck was in and talk to the owner about its history. Yeah there is always the unknown, little white lies ect. but there is at least info there. I'm not trying to force you into buying a new hitch, just giving my opinion and hopefully giving you some points to consider.