Please give us your computer specs, this will aid in finding the best fix for the least bucks!
I have 2 computers, both have the same problem when near large convoys & it's not the video, both have only 1gig ram & the best way to fix this would be an increase to 2 gig!
I haven't bothered as the slow down is not bad enough to warrent the extra expense.
Once again IMHO.