While flying in certain planes I losing some functions. This especially seems to be happening when flying the Captain Sim, C130. After a certain time, lets say 15 minutes, but could be more or less, I'll lose the screen on the GPS (it will go black (blank). Also the autopilot will quit working (not necessarily following a course, but just maintaining alt). The landing gear won't respond either, but I found out if you keep hitting Alt + G, it will then toggle down. (One time it just continued flying for awhile, and then corrected itself and operated normally). This same sort of thing happens occasionally when flying the PMDG's 747x, but there is no GPS screen. Usually just before landing, and even throttles don't respond. Doesn't do it all the time, but seems more prevalent after not flying it for awhile. Also had the same symptoms while flying Flight1's Cessna 172, but not very often. I do most of my flying with PMDG's 737, and seem to have no problems with it.
Specs on my system: Intel I7-3770K CPU @ 3.5GHz, 16GB RAM, ATI 7970 graphics board, Win7 Professional, Service Pack 1, 64 bit, and Saitek yoke and throttles. I'm running 4 monitors off my graphics card, but don't seem to have any performance problems with it at all (in other words all my scenery and stuff is nice and smooth, no jerkiness at all).
Any help and/or advice would be appreciated, and, thanks in advance.