At sealevel with a DA-50 and PT 22X8 I got as high as 7200 RPM on the ground on the first tank. You should get 6900-7000 with this prop at 4800 feet. I also had a DA at 6800 feet where I live and got 6800 with a BME22X8 on the first few tanks.
You may want to look at your muffler, too. I recommend the stock muffler over anything else. If you are using a Bisson, you are choking a good 2-300 RPM out of your engine. You can make that better by cutting off 1/2" from the exhaust tips. If you are using a slimline it isn't as bad but still not as good as the stock muffler, IMO.