2000 Venture RPM limited when cold

I have a 2000 Venture at 160K miles. It starts and sounds great until you try to pick up the RPM. It is fine up to about 2500rpm but then it is like a rev limiter cuts in and the motor surges up and down until you back of the gas and then it revs Ok. Once the motor reaches normal running temp it will run as normal with good performance and very smooth. I have replaced both O2 sensors, new AC Delco platingnum plugs and wires, and new fuel filter. No code faults are indicated. The car ran great one day then the next this problem occurred. Any ideas?