It could be a couple of reasons why your MasterTow Dolly is chucking when applying brakes.
I recommend checking the brake fluid levels and ensure it is not low. I also recommend checking the ball and coupler, and ensuring that you have the correct size ball, and that your ball isn't loose.
Finally, you could have a partner ride alongside you and examine the chucking, it is possible something on your hitch is loose and could be causing this issue. view full answer...
It sounds like the circuit board for your MaxxFan Deluxe Roof Vent w/ 12V Fan, Thermostat, and Remote - Powered Lift - 10 Speed # MA00-07500K is the issue.
I recommend replacing your circuit board with the Replacement Printed Circuit Board for MaxxAir Manual Lift RV Roof Vents # MA10A21276K. view full answer...