Prius Gen2 Hv battery always 1 bar on highway, struggles up hills

2008 Prius MFD displays Hybrid battery normal driving in town, speeds below 50mph, flat terrain. However after getting on highway MFD show battery drop to one bar and stays like that until exit ramp. Any hill of a couple hundred feet or greater, car struggles to get up, very little power, if going 75mph at bottom, at hill crest only at 60mph, cruise control disengages mid climb.

No check engine nor red triangle lights.
Tech stream scan reveals no codes, current nor pending.

Some considerations:
-I also have 2005 Prius and did a swap of hybrid batteries and batteries working good in 2005 car so I can eliminate that possibility.
-replaced spark plugs, ignition coils, PCV valve, engine air filter.
-12v battery tested good on mfd with and without load.
-Inverter coolant churning as should.
-No strange engine sounds nor leaks.

Things(possible culprits)I’m thinking about:
-mg1 and mg2
-Inverter
-ECMU(main)

Any ideas/suggestions greatly appreciated.
I have read through a couple hundred threads at this point and haven’t found exactly the same scenario with answers/solutions.