question about power window switch

i have a 92 chevy lumina apv with power windows and doorlocks i think the motor for the window is weak a friend thinks the switch is bad. if the weather is hot and sticky the window will go up about a 1/4 of the way then stop it then takes a good 15 min or more to go the rest of the way i have to wait then try again it will go up some more then stop then i have to wait again and so on till it finally goes all the way up. however when the weather is cooler the window will either go all the way up or go almost all the way then i have to wait less time and it will finish. it almost always goes down all the way first shot. my friend has based his opinion of the switch on the fact that the passenger side switch is tempormental it has to be fooled with in order to work and the powerdoor lock does not work at all. i would apreciate input on this the window switch is expensive but easy to replace, the motor isnt much cheaper but is going to be much more difficult to replace. i only have money for one or the other, so id hate to replace an item that doesnt need to be replaced.....yet