"...my e brake won't hold" --- "is it just the size of the tires and truck?"
Naw..., there's a ratchet above & behind the E-brake foot pedal..it (tooth) can get worn., along with a couple other components.
(you should hear it "click-click" as you engage the pedal.
Two nuts on the firewall., (pard. the pun) & one bolt on the dash & the E-brake assy. will come out for inspection.
1 banana job....! B)
OH...! if the ratchet is working & shoes won't lock on rear wheels.., your cables may not be installed correctly/hooked up to shoes, etc.
Another point to check is the bracket the cable hooks to/thru under the veh. under the driver seat. Sometimes they break lose fr. the weld....