Check the drive pulley on the engine, it may have been coated with congealed oil possibly from a leaky bottom crankshaft seal. If so, and if the engine has been using oil, or you find an oily puddle beneath it, that may be the problem with the belt. Park the tractor on a large piece of cardboard box flattened out, when ever you are thru using it, and you'll soon see if it is leaking there. The seal is not expensive, and can usually be replaced without taking out the engine. Note: I say "usually", but in practice--not always. Also, with the engine NOT running, see if you can stick a finger on the upper side of that pulley, to see if it is leaking at that seal. Rust in the pulley sheave will cause a jerky drive pattern, too.

Transmatic (CVT) is actually a pretty good transmission, considering MTD cut a lot of corners elsewhere in their designs. For example, the single speed Peerless rear axle is definitely weak. That said, most important thing is to replace belts with OEM. The sizing is close, but slightly different from standard 5L or "B" power transmission belts. The rear belt is 954-0281 and is 44 7/32 (comm'l 5/8 x 44" B41) and the front belt is 954-280A (5/8 x 53, B50). I've used commercial, sometimes with success, and other times had to go back in and replace. Since you're already having issues, I'd stay OEM. Since you're not getting into the lower speeds, I'd check the sliding flange of the two-part transmatic pulley. May need to be lightly lube to get full range of motion. Brakes is not a transmatic problem per se, but could be an adjustment issue. Check to two pads on the transmission disk brake and make sure the pins aren't frozen and corroded. Take apart, polish, relube and assemble. You might also need new pads 917-0678 (about $4 each). If you need to rock the tractor to shift forward and reverse, the clutch may not be fully disengaging the transaxle. Lastly correct deck belt is 954-0329A which is 69 9/32". Can usually substitute commercial 5/8 x 69 or B66, but since you're having trouble the additional 9/32" of the OEM may make a difference.

OK. Listen up people. In the 60s oils were developed for Jet aircraft which operated in the extreme cold (like -50) at 35000 + feet and yet could handle the extreme operating temperatures ( 300 + degrees ) generated by the jet turbine engine, basically a giant blowtorch. These are what we now know as "Synthetic" oil or hydraulic fluid. I live in Northern Canada where in the winter I have experienced -55 degrees F. and summer temperatures of 120F. Cold Temperatures such as this cause oil not to flow where needed, to seals and bearings and bushings, and to seize or wear out or just break or don't function. Synthetic fluid continues to flow at these extremely low temperatures, therefore the components are lubricated, do not dry up, and do not break. As well the load on your starter is less, quick start without overheating your electricals. Very high temperatures (+80) have a similar effect on normal oil by causing it to break down from the engine/system heat into it's constitute parts and thereby lose lubricity. Synthetic oils do not break down inl heat, again all the parts are lubricated and can withstand the loads on them. I know it is much more money to run Synthetic fluids, but the savings in time, Repairs, and frustration is worth it. Synthetic fluid costs more, but your change intervals are longer, therefore it works out to about the same. When you first use Synthetic you will find everything starts to loosen up and work much easier. It is important to choose the right Synthetic for each load application. Here in Canada, Toyota now uses only their Synthetic at about $5.00/ quart on their vehicles since their research proved that it worked better, and they had fewer service recalls. I change my Synthetic every three months, my hydraulic fluid once a year. At -40 my Kubota starts every time and runs better than the day I bought it used. If you can't afford to use Synthetic all the time, just replacing one quart in your engine with Synthetic will cause wonders. All the best, lubricate and save on repairs.

Remove the deck so you have a good unobstructed view of the ground drive belt system. Have a helper sit in the seat and push down on the clutch/brake pedal while you examine all the linkages in the mechanism from below the frame. You are looking for worn or loose pivots, pins or anything that can limit the travel of the components that put enough slack in the ground drive belt for the transmission input pulley and shaft to become "unpowered" so you can shift. Have you also noticed the clutch engaging at a lower pedal position when you try to get moving from a stop? That can also be a symptom of the same issue. If you have recently changed the belt and did not use an OEM spec belt there is a chance the belt is a fraction too short. Basically, something is causing a bit of power to be applied to the belt when the clutch is pushed down. Here is a link that might be useful: 917.272751 OM