Lose throttle in higher gears

I have a similar problem with a 2013 Kenworth T800, I believe it is a ISX13 with a Eaton 13 speed.
It has 323000KM on it.
It was governed to 105km when I purchased it New, I had this removed at a Kenworth dealer.
Now when I am in 7th High, I will lose throttle at around 90KM if I do not shift to 8 low before that.
Then in 8 Low I will lose throttle around 100km if I do not shift to High before then.
When I lose throttle the speed has to drop quite a bit before the throttle will respond again.
I say around those speeds because if you are under power going up hill say, it will cut out at 95 and 105 km or so.
If i was coasting or say going down hill it will cut the throttle the throttle out at 85 and 95 km or so.
It acts to me as though the higher gears still have a limiter on them but there is not a top speed limiter.

 

Thanks for the information!