Please Help: Trouble with Express L6 - less than 1 year old

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All,

I need help. I have a 2018 (I think) Express L6 that I purchased last spring. This past fall I had Bob Boyce work on the controller - to the tune of significant performance upgrades... I'm HOPING that isn't related to my problem below, but really need some advice:

In THIS THREAD I detailed an issue where my lights would go out upon pressing the accelerator after only 20-25 mins pulling my kids around the yard on a sled in the snow. The issue was blamed on the cold temperatures and that draining the batteries quickly. I'm afraid the issue is different than that:

Last week the temps were in the mid 40's - not cold - and my cart is stored in a heated (60 degree) shop at all times. This means that the batteries start at at least 60 degrees (they're coming off the charger) and shouldn't get really cool in 40 degree weather - especially only being outside for 25-30 mins...

In these 45 degree temps, on snowy FLAT ground, I pulled 4 small kids in a sled just under 2.0 miles before I noticed the power dropping off significantly. Once I noticed this, I had the kids get on the cart, and at a snails pace (getting off the cart just go it could go up a hill) drove about 1.5 miles back toward my house before I had to ultimately tow the cart home.

Upon returning home, I intentionally didn't connect the charger to the cart. I figured I'd post here first to see if anyone had advice or wanted me to check anything.

4 miles range at in 45 degree temps coming off batteries that were warm is not normal. What can/should I do to pinpoint the issue? Noting that this cart is less than 1 year old, and should still be warrantied.

Please help.

Thanks