C130E's use GTC's, HC130's (17XX) use APU's. Also, different airconditioning packs.. Most operators of C130E's probably wouldn't care about the weaker AC pack on the E's, but an HC130 will spend a ton of time flying at low altitudes to do  search and rescues.....were the E's AC pack will do nada for keep the temps cool. I flew on a few 15XX's with the old AC packs while running the sensory gadgets, even stripped down to my skivvies, I was stil sweating my tushy off....note the 15XX are truely E's, although some were upgraded with better AC packs off the 16XX from Hawaii that were retired early because of corrosion issues, but reguardless...15XX were put in E-City for a reason.....it's much cooler there.