Do you need a class a cdl to haul a triple axel trailer with an f350 in Texas?

Depends. If you have a Gross Combination Weight Rating (that's the combined Gross Vehicle Weight Rating of the truck plus that of the trailer) in excess of 26,000 lbs., with the trailer itself having a GVWR of more than 10,000 lbs. (which a tridem gooseneck will have), then yes. And that's not just Texas - that's a federal law.

Now, there are some exceptions to this, in instances where it would not be considered a commercial vehicle. If it's registered as a farm vehicle, is being used for the purposes of that farm, is operated with a 150 mile radius of the farm it's registered to, and is not operated on a third party, for hire basis, and is operated by the farmer, immediate family members of the farmer, or direct employees of the farmer (W2 employees, not 1099 contractors), a CDL is not required.

Likewise, if it's a recreational vehicle (e.g., travel trailer), a CDL is not required, so long as it's not being transported on a for-hire basis.