First off welcome to the site from California.
There is no adjustment on the steering wheel as far as pushing it down toward the cab floor without modifications. I have seen people swap steering columns for different one's that are shorter, but I do not know what type of vehicle they came out of, just seen some at shows.
I would check the ground on the sending unit itself first for the gas gauge problem.
Is your heater core going out or partially plugged up ? Sounds like that may be the problem, my trucks never have had a problem with not being hot enough, even in the mountains in the snow.
More members will chime in and give you some more idea's.