Tired EH29C Engine?

[Cjinfl]

I have a 1996 EZGO Textron S/N 947670 MFG # F1196 with a Robins EH29C Gas Engine. I put a Jake lift kit on it and 21X10.5-12 Tires. I adjusted the governor right to the harry edge of its limits. I can only get 19 MPH out of it on flat ground. It is street legal and people get pissed when behind me. It also really slows down going up hill. I checked the compression on the cylinders today and they are good at 150 and 165 psi. It does use a bit of oil and one of the spark plug had some carbon on it. I have been told to change the springs in the clutches and the gears in the axle. Have thought about putting a bigger engine in it but not sure what will fit. I want it to do at least 30 mph and not slow down so much going up hill. This cart is our main transportation while we stay in Key West.
Any suggestions will be considered and looked into.
Thank you in advance
Charlie