I drive my 1995 Eldorado Cadillac for 30 miles it will lose power up hill

With the hot temp 100', it could be vapor locking..I try not to use the ac when driving up hill or steep inclines for very long. Did this happen during the cool part of the year in the same area? I found out not to fill the gas tank full, I leave it above half, therfore the fuel vapors can escape during hot weather, and when it does it again, pull over an open the gas cap very slowly and be careful it will be under pressure. If so, changing the gas cap may help too. Hope this helps!