just yesterday i filled my tank up to the brim with gas and the gauge only read a little over 1/4 tank. as i was driving around all day yesterday it seldomly would read full and then go back to the 1/4. what might cause this? where is the float on these tanks (1972 in cab tank).

The float mechanism is in the front center of the tank. It is removed by sliding the retaining clip around. Don't remove it while the tank is full.
You may have a faulty sending unit (inside the tank), or a poor connection, or a poor ground.
Start at the tank, checking each wire connector, and work towards the dash. Rust and corrosion inside the quick connector wire clips may be at fault.

so youre saying that the float mechanism is at the front top center of the tank? could i just move my seat up to get access to it?

I had to pull the seat out. But if your seat back folds forqward you might be able to pull it out with the seat in place.