For your logic to be correct then two things would also be true. The depth of a 80 gallon tank is much greater then a 19 gallon tank. I think what you will find out is it's not the depth but the length and width that will be where the extra fuel is stored in a RV.
Second, all 460's would be having that problem from day one. Mine never did as many others didn't. The fuel pump of that vintage did have a design flaw, but most have been replaced. The new ones have a four wire connector as I remember. If you have the old pump you will need the new connector also.
Yes fuel pumps start to fail when they get hot. This might be your wake up call from a good 'ol girl trying to tell you "best fix me now before I strand you." That pump may be generating more heat due to worn out internal parts, or bad electrical connections.
