Engine lacking power over 2000Rpms

[vdubin 0]

Im almost at my witts ends with this issue..

Mk3 96 Vr6

What Ive done

Cleaned throttle Body.

New leads & plugs.

Checked Coil pack ( all good )

Had Vagcom over it twice No engine issues came up.

Tried my mates cold Air sensor.

The Issue

After driving the car for around 5 mins all of the sudden it lags in power any thing over 2000Rpms or 40Kms If I put the foot down it just struggles ( mate thinks its limp mode ) Im trying to work the issue out my self and save time & money + my machanic is flat out atm but im at a point of cracking it lol PLZ anyone had this issue before or can help me?

Im thinking Coolant sensor ?