2001 lionel joshua lionel cowen challenger

I can't answer your question, but I'm assuming it did this also after a reset?  If you haven't done a reset, I'd try that first.

Let us know if it works.

The reset from the manuel is this:  push eng, ad number ,press set push aux and enter code 74 and turn off power.  shouldn't there be a press set after the number 74?  The manuel does not say so.  I did this and no change.  Remember this is a 2001 engine.  I have heard of the legacy lurch, is this it?

NO set after 74.   G

The lurch the first time after power-on is the infamous Odyssey lurch.  AFAIK, there is no cure for it, but not all Odyssey I locomotives have the issue.  The CCM would solve it, but I just live with it as it only happens after a power cycle.

I had this engine and it had the lurch.  Was considering upgrading with ERR cruise commander and new RS 5 but decided to sell it as is and purchased a MTH Challenger.

Some TMCC locomotives 'lurch' and some don't.  Fortunately, mine does not.

Then again, I've only ever ran it with Legacy.  Be interesting to see if the OP's engine would respond better to the 990.  Not sure if he's using a Cab 1 or 2.  Assuming a classic TMCC system.

Maybe he could post a video?

I just did an ERR upgrade on a Weaver FEF and I'm blown away by how smooth it operates.  And, I still have a few tricks left for it!