2002 Subaru WRX 5 speed manual. Whenever I'm sitting around 2500RPM for example and I give the car full throttle, the RPMs will shoot up to about 5000 with hardly any acceleration and then fall back down to 2500 and the car will then begin to accelerate. I'm thinking the clutch is starting to slip but could it be something else? Also after I let off the throttle sometimes the car will take half a second to stop accelerating. Almost feels like the throttle body is staying open for a split second after I release the throttle.
When you get your foot off the clutch, there is(or rather said there should be) a fixed connection between your engine and your wheels. If you see a rise in rpm without the car accelerating, there is no other possibility than that the connection has slippage somewhere. And while the clutch is the most plausible option, i also think it's the only possible option. So i'd take a look at your clutch because to me, it sounds like its totally worn out. The only other option is that if you heavily upgraded your engine without upgrading the clutch. Then the clutch is simply not capable of handling the higher torque form your engine.