This is a bug that affects gingerbread stock roms, it is called memory-leak...there is a certain process in background that wastes all the free ram we have in the phone, so after some time (tipically 12-24h) our phone begins to slow down. It will be pretty unusable, you have to restart the phone.
Froyo roms don't have this bug. After 50h of runtime my phone is still quick and smooth. Try nostalgia by topogigi.
Or try cm7, but is a battery-hungry rom.
Inviato dal mio LG-P990 con Tapatalk 2