Really long pauses in FS2004

I've recently done a complete re-install of FS2004, the only addons I have running at the moment are Gary Summons UK2000 part 7, Extreme Gatwick + Glasgow and Aerosofts Heathrow. I also hae Level D 767, Flight one 727 + ATR42 and project Tu154m.I seem to be getting really long pauses of upto 30 seconds!! whilst flying around usually about 3-4 mins after I'm airborne, all the textures go grey and then eventually they come back...my system is as below.Thanks for reading!