HOW TO ADJUST DRIVE BELT

There could be a few possible reasons for your Trojan Runx treadmill to have this issue:

1. Belt tension: The treadmill belt may not be tight enough, causing it to slip and lose speed. You can adjust the belt tension by using an Allen wrench to tighten the bolts at the back of the treadmill.
2. Motor: The motor may be overheating and shutting off, causing the treadmill to slow down. You can check the motor by opening up the motor cover and looking for any signs of burning or overheating.
3. Motor brushes: The motor brushes may be worn out and need replacing. This can cause the motor to run slower and eventually shut off.
4. Power supply: The power supply to the treadmill may be insufficient, causing it to lose speed. Make sure the treadmill is plugged into a dedicated circuit and not sharing power with other appliances.

If you're unsure about how to diagnose or fix any of these issues, it's recommended to contact a qualified technician or the manufacturer for assistance.

Check drive belt proper tightness

It depends if the deck is a belt driven model or Direct Drive.

If it is a belt model then it's possible that the belt is not in the correct place. Some decks have speed preset control for the two speeds. Sometimes it can be found hidden under the deck. It will be adjusted by a small screwdriver. You will of course have to get the speed right yourself. The preset can sometimes be found inside the deck. Most likely accessible via the underside of the deck.

A direct drive model has separate circuits for the two speeds and would require a technician to sole the problem.

Your Sd card maybe too slow
I assume you know how to set your speed
your sd card is buffering to slow for beginners.
Spend more money on a new card.

Some self-propelled mowers include a speed control, but sometimes it may seem that no matter how you adjust it, the mower just creeps along at a snail's pace. Most likely this isn't a mechanical malfunction, but an adjustment is probably needed.

Very tall or thick grass can bog down a self-propelled mower, but adjusting the height of the blade may allow it to roll through and cut the grass at normal speeds. If the blade is low, the amount of cutting required may slow down the movement of the entire mower. The frame of the mower may also stick in the high grass. Raise the blade little by little until the mower rolls at the appropriate speed. Going up hills may cause a similar response.

It's possible the drive belt on the mower can slip. Inspect this part to see if it is loose or cracked, and replace the belt to restore power.

hydrostatic transmission there is only one throttle setting and that is WFO. if it is running slower than it used to, and the drive belt is snug, then you are looking at a failing transmission.

There are two possible causes, depending on if the deck is belt driven or direct driven. Sorry I don't know which with yours.
If it's a belt drive then the belt has come lose and should be replaced. Or the motor or power supply to the motor is faulty. Make a note of how the belt fits before you replace it.
With a direct drive it's either the motor or power supply to it that's got the fault.

the belt will not adjust the speed unless it is slipping, therefore will slow down not speed up.
there should be a speed playing dial. for lp or 45's.
or have you had it repaired. if someone replaced the pullies on the drive or driven end this could have change the ratio and speed.

You need to adjust the gas pedal. Info should be in the owners manual. I have it in my Troy Bilt Bronco manual. It say to adjust it in my book after replacing the trans drive belt. Maybe that will help.

put oil or grease all the shafts and bearings inside and out, if possible adjust the cutter blade contacts.