There are several different types of dirt that can get into the carburetor.
If the gas tank had dirt in in, and they didn't clean the gas tank or replace the fuel line, there could be dirt in the carburetor again.
Also these new engines are set to run very lean so they will mee the new EPA regulations. Many of these engine never really run correctly...especially if they are used in higher elevations.
The only real way to make these carburetors work correctly is to take a jet drill and enlarge the main just just a little. We are really not supposed to this, but sometimes it is really necessary.
The engine is just running lean. Dirt is the leading cause, though.
In most cases, dirty carburetors are not covered under the warranty. That is because the issue was not caused by a defect in parts or worshipship.
Most of the repair shops tend to be somewhat lazy and do not clean the tanks and replace the fuel lines. They just usually want a quick fix. Then when it doesn't work too long, they have to do it again.
I would reccommend that you take it back to the shop that you had do the work and let them know that it didn't stay fixed. Although some shops may not do anything about it, most good shops will at least try to make it right once. Give them the chance to help you. If it doesn't work correctly when you get it back this time, then I suggest that you contact Troy-bilt and tell them the whole story. They may give you some additional advice or tell you a different dealer to take it to. This is actually not a Troy-bilt issue, but it is an engine issue. If you can find the brand name of the engine and the model and serial number of the engine, you can also call the engine manufacturer and see what they have to say. Sometimes they will authorize a "Good Faith" repair even if it really is not a warranty issue.
At our shop, we really go out of our way to help the customer. Iwish you were near us.