Civ 4 worked fine for me since it came out, through every patch, expansion, all that. In the last two weeks however, it just suddenly started to exhibit some really poor performance. The telltale sign is that whenever I move a unit, when it gets to about halfway to its destination, it will pause for a split second. I can play for a few minutes normally before the game really starts crawling- the map movement is jerky, diplomacy animation stutters, units move slowly.. everything is slow. It gets worse as i get into later ages, but i was last playing on a small map, 7 civs, certainly no reason for it to have problems.

heres my computer:
Pentium D 3.0ghz dual core
4gb ram
geforce 7600 GT
120gb hard drive
winxp

before i could run the game on huge maps, 18 civs, no problems at all. im running warlords 2.08, though the problem also occurs in civ 1.61.

heres a list of solutions i've tried-
deleting the cache before every game. no improvement.
updating video card drivers- marginal improvement
defragging
manipulating virtual memory (started at 2500-4056mb min/max, put it up to 4056-4056min/max)
uninstalled and reinstalled the game
scanned for ads/viruses; i watched the performance tab and saw no outstanding memory usage, no strange applications, nothing.
turned off virus checker.

the only improvement from these was that at start up, the game runs better. but hten it still gets bogged down just as quickly.

i really have no idea what else to do. also i dont know why this happened. i didnt change anything on the computer- no new software, drivers, etc. it just started out of nowhere. if anyone can help, it would be greatly appreciated.