It could be that it has low oil pressure or it has a transmission that isn't quite working properly or the transmission fluid and filter needs to be changed on it.I'd at least went to check the gas pressure or change the gas filter , check the air filter and on those they tend to end up with clogged or gunked up oil screens on those so I might try using a STP oil flush on it just follow the instructions very carefully.
One suggestion in the mean time when dealing with such hills is try turning the cruise control on before the hill and see then if it goes up much better.
Hope that helps and best of luck.By the way if you know someone that can check the engine etc I'd for sure check the engine compression and oil pressure and gas pressure bec even a weak fuel pump can cause that problem.
