Lawn Tractor Question

I have a Craftsman 42" Riding mower. I had this mower for about 10 yrs and it has always been maintained and has served me well every season. Last season I had this mower sent to the local lawn tractor repair shop and had $700 worth of work done to the mower including new steering shaft and front end components, tune up, valve adjustment, pretty much overhauled. The mower was operating awesome when it came back from the shop in August. I put it up for the winter, drained the gas and put Stabil in it. Well now the issue: I used it a couple times this season and it was working without any issues. Went out to cut the lawn Sunday, Mower started fine. Started cutting and made a couple passes and the mower started to sputter and I was able to keep it running. Made another pass and it died. It will not start but for 30 seconds now. I took off the fuel line and verified that there is a good flow into the carb. Checked Spark plug for spark. There is spark. Replaced the fuel filter, took off carb and sent it out to the lawn repair shop. They put in a new needle valve and seat and a new bowl gasket and pressure tested. Well, I picked up the carb from the mower shop tonight and installed it back on the mower. I fired it up and she was running strong, for about 5 minutes. Then the mower started doing the same thing sputtering and died. The gas in the tank is fresh. The tank and lines are clean. the filter is brand new and there is gas getting to the carb. I am stumped. I cannot figure out why this mower seems to be starving for fuel. It is a Briggs and Stratton 17 HP Vertical shaft motor. Any suggestions? Throttle cable is operating properly. Any help would be most appreciated. Thanks, maniac