Cub Cadet LTX 1040 / Odd Forward and reverse Issue

Have an issue with my 2009 LTX1040. To start there is new pulleys, variable speed pulley, various springs and new belts put on over the past few years. Now for the problem, with the deck off it moves forward and reverse at any speed, slow to fast and low throttle to fast throttle with no issues at all. I put the deck back on, hook everything up and it barley even moves forward and reverse. I have adjusted the cobra head rod for foot pedal tension multiple times with the same result. The variable speed pully is new and as I watch it work it does what it is supposed to do. This issue has slowly been getting worse over time. Could it be worn out double pully shaft that attaches to engine wearing out? just don't know.

Can I ask you a question when you look at the variable speed pully with both belts on will the plate slide?

Wouldn't hurt to inspect the engine stack pulley for wear. They can get a groove worn into them that will act like a belt that is bottoming out in the pulley groove causing slippage.

Have you tried going up a incline with the deck off after the drive belts gets warm???. This is too see if it will pull ok instead of just seem ok across flat ground with cold belts. I've seen cold belts pull ok for awhile AND both belts HAVE TO be replaced as a set.

Simply installing the deck should not have anything to do with travel unless for some reason it causes the drive belt to get some slack. (is the engine mounting bolts tight..(especially the rear ones)

Try hooking your heel onto the clutch pedal and pull back and see if it speeds up. This puts more tension on the front drive belt. I've seen the SPRING LOADED variator pulley not slide freely. I'm not talking about the center sheave, I'm referring to the spring tension sliding rotation of the pulley assembly.

Can you post up the exact model number of the machine.
Lots of variations to the LTX1040 is why I ask.

The engine stacked pulley does get a wear groove in them with age and high hours. Other considerations are a stretched belt, especially if aftermarket, or a tired main belt tensioner spring.

I have had older units that I had to add an additional tension spring to.