Do you see any bars light up in the charge gauge when you take your foot off the gas or step on the brake? If so, I would suggest checking the 12v battery, if it is going out then the 144v pack will try and keep charging it. I have a 2002 and replaced the 12v a few months ago and my SOC now rarely drops more than 1-3 bars during normal driving.
Easy test: drive at ~35mph and take your foot off the gas, you should see 4 or more bars light up and the car should slow down almost as much as if you were braking.
I would be surprised if the 144v pack or something else was failing and not giving a code that the dealer could read. You can check if there are any temporary codes by turning the key to ON and watching the Engine Light. It will turn off after about 20 seconds if there is no code or it will flash a few times if there is a temporary code. That could at least be something to approach the dealer with.
Easy test: drive at ~35mph and take your foot off the gas, you should see 4 or more bars light up and the car should slow down almost as much as if you were braking.
I would be surprised if the 144v pack or something else was failing and not giving a code that the dealer could read. You can check if there are any temporary codes by turning the key to ON and watching the Engine Light. It will turn off after about 20 seconds if there is no code or it will flash a few times if there is a temporary code. That could at least be something to approach the dealer with.