Gmod lags on sp

hi
my gmod lags on sp in maps like mobenix evocity downtown etc…
it doesn’t lag on hugeflatconstruct and flatgrass.
i already tryd to lower my directx lvl but that does not work
system:
windows 7
8G ram
1T hdd
nvidea gforce (i don’t remember the serie i think 260 or something)
intelcore i7 inside

BUT
on my sisters laptop with has
windows vista
2G ram120G hdd
and ati video card or something it doesn’t lag on sp and mp in any map
plz help me
Thanks already

thanks for the help --’

I have the same problem. I think you just have to lower your field of view range.

It’s probably an addon if it’s only doing it on Singleplayer.
Try cleaning out most of the addons you don’t need, or all of them.

Sounds pretty unusual. I hate trying to sort out arbitrary problems like that so i’d just uninstall everything and start from the top. If it persists you may have to look into it a little further though.

i have the same amount of addons like on the laptop and with my pc it lags

Hmm, have you tried reinstalling GMod?