I don’t know exactly what the issue is, so I’m going to rapid-fire some possibilities and you can shoot them out as you like:
What is the angle of your frame? It almost sounds like it is too steep.
Is your sled ligher than it should be and doesn’t plunge?
what are you cutting? Is your bit dull or your feed rate too high?
Are your chains parallel to the work surface?
Is your sled tipping up (bottom lifting as the sled moves up)?
Is your sled pulling away (top lifting near the top of the frame) or as the sled moves down?
Most of these point to a balance / chain / weight issue except for the bit. if the frame is 15 degrees off vertical, it should be fine. If it is 10 degrees, it will lift and tilt easier. Put a 2x4 under the front frame legs and it should tilt back roughly 5 degrees if you have a standard frame. If the ring is too low and the motors are too far out from the board, put in another spoil board to move everything out, but this is less likely. If the ring is too high and the motors are too far in then it will tilt as well. Start with balancing the sled so when you hang it from the ring, it hangs at the “right” angle (get it, the one on the right?):
then check your chains are parallel and adjust the motors if necessary. Good luck. Please report back what works.