Getting Stutters with AS6.5

Hi, Ive been using AS6.5 for many many years now and it ran absolutely great with my older video card and 2ghz dual core cpu. Now that keep the same memory and mobo, I only upgraded my video card from a 512MB Radeon X1950PRo to a 1gig memory Radeon 4670 (AGP) card and the CPU from a 2.3ghz dual core to a 3.06ghz dual core, the sim runs nice and smooth with a constant frame rate of 30 (locked). However I have noticed when using AS6.5 and there are clouds in the area, the frames will start jumping from 30 to 17, 30 to 24, 30 to 13 for example and I start to get stutters that wont go away unless I go back to windowed mode and then again to full screen. I have dont a couple test flights with the default weather program in FS9 (auto update ever 15min) however I dont get the stutters after around 30 min for flight. I do want to use my AS6.5 again. I have not changed any settings, in matter of fact I have not touched my AS settings for years. I believe if it aint broke, dont fix. Any ideas?

My apologies, dont know why there are 2 more topics of the same things from me. Please remove the other 2 topics.