Pat I raise the deck up and start the mower while the tractor is traveling
forward.

i certainly would take the lawn tractor back to the people that did the maintenance because it sure sounds like your carb is loaded with junk like pat has mentioned.
if its messing up now and u are about to put it away what will it be like when u need it again because if its cold out and u get condensation and junk in your machine it will be 100 times worse when u go to use it again.
so yup i sure would be on their case make them take the carb right off and clean the thing properly thats supposed to be part of a maintenance program for lawn tractors after all isnt it. good luck. sockiescat.