John Deere SRX95 will not stop after I take my foot off the gas pedal.

[mikelkraft]

I had my mower service and they replaced the drive belts and a pulley. After I got it back the mower goes twice as fast, which is OK but when I take my foot of the gas pedal it does not completely stop. This occurs in forward or reverse. I have to quickly shift gears (forward/reverse) to keep from running into something. The mechanic said that is just the way that mower is and can do nothing about it. This never happened until after they serviced it by replacing belts and a pulley. Is there a fix for this? It does not seem correct that JD would put a mower on the market that operates this way. It seem too dangerous.