Jup, probably not the motor mounts.
I had the same problem (And still have) with my 88 Turbo.
A lot of vibrating at about 3000 rpm or at high loads on low rpm. My mech just ripped everything from the drivetrain out and noticed the driveshaft bearing (hard to explain, but it holds the main driveshaft in place at the clutch) was completly wasted.
So, we replaced it with a second hand one. Most of the annoying vibrations and drivetrain noise was now gone. But, still the vibration in the stick remained. I replaced a couple of rubbers at the gearstick which reduced the vibration a LOT. But, it's wearing out again pretty fast as there is still vibration.
And, i think i know why:
The gear linkage for a 944 is very long (tranny in the back) and this linkage is probably sensitive for some vibration in a certrain frequency range. Of course, the engineers designed the car in a way that the frequency of the engine, driveshaft and gear linkage would not go in sync.
They did this with the balancer shaft in the (very unstable) 4-cyl engine, special bearings on the driveshaft and some rubber dampers all along. But when stuff starts to wear out, frequencies will strengthen each other.
Solution: replace all the dampers and rubbers in your gear linkage etc. It will keep out most annoying frequencies.
PS: Scuse me for my terrible english, but i'm trying
