2000 Pontiac Grand Prix Engine Trouble

My Troubles with my engine are as follows. I start the car it runs fine while idling while revving rpms commence to shake while still in park. Example: flucuates between 2 and 1 rpm very fast and violently. Along with that heavy knocking. Has had oil changed as well as oil filter.

while driving when changing from first to second gear at peak of first gear. Rpms begin shaking and flucuating also. Between 2 and 1 rpms as well. Problem has just started occuring once car reaches 40 mph its fine as long as I dont accelerate or lose acceleration causing me to accelerate again. Have no idea what problem is.