Allison 3000 3-4 shift

[MonacoMarc95]

Hello. I am having some issues with my 96 Monaco Dynasty and am trying to determine if I have a trans issue or, an engine related issue. Going back a few months I had noticed that my mechanical 8.3 was down on boost pressure. Typically, I would see pressures at/above 30 psi ( I have a fuel plate and some other mods that were done by previous owner). Last few months I have only seen a max of 25-28 psi. during this time, my trans has had some strange shifting characteristics that seem to have developed, particularly in the 3-4 shift. After being up and down this coach, I realized that I had a leaking exhaust manifold gasket. Ahh! this explains the decrease in boost pressure right? Nope! $1900 later, still down on boost and now have this 3-4 shift hangup. Some refer to this as "flare"? What I notice is that as I accelerate in 3rd gear I see a loss in boost pressure as much as 15psi right before the 3-4 which the trans seems to "hangup" and then the rpm jumps 3-400 rpm and then it will shift. I have checked for codes on the shift pad and there are none. New trans was installed back in 2013 and has about 20000 miles since. fluid is Transynd and looks/smells like new. I am lost as I do not know if this issue is trans related or engine related. I have been told that a reduction in engine power will cause these transmissions do some weird things. Any thoughts or things to look at or, do I need to find an Allison dealer to diagnose the problem? Any help is appreciated.

[NHRA225]

I would check the TPS -Throttle position Sensor-- Its in line on your Throttle Cable- and needs adjustment from time to time depending on mileage. There's also a Brass bell crank on the end of that cable that wears out.- I seem to change mine every 75,000 miles or so. It won't throw a code but certainly affects shifting .

[Cat568]

Originally Posted by MonacoMarc95

Hello. I am having some issues with my 96 Monaco Dynasty and am trying to determine if I have a trans issue or, an engine related issue. Going back a few months I had noticed that my mechanical 8.3 was down on boost pressure. Typically, I would see pressures at/above 30 psi ( I have a fuel plate and some other mods that were done by previous owner). Last few months I have only seen a max of 25-28 psi. during this time, my trans has had some strange shifting characteristics that seem to have developed, particularly in the 3-4 shift. After being up and down this coach, I realized that I had a leaking exhaust manifold gasket. Ahh! this explains the decrease in boost pressure right? Nope! $1900 later, still down on boost and now have this 3-4 shift hangup. Some refer to this as "flare"? What I notice is that as I accelerate in 3rd gear I see a loss in boost pressure as much as 15psi right before the 3-4 which the trans seems to "hangup" and then the rpm jumps 3-400 rpm and then it will shift. I have checked for codes on the shift pad and there are none. New trans was installed back in 2013 and has about 20000 miles since. fluid is Transynd and looks/smells like new. I am lost as I do not know if this issue is trans related or engine related. I have been told that a reduction in engine power will cause these transmissions do some weird things. Any thoughts or things to look at or, do I need to find an Allison dealer to diagnose the problem? Any help is appreciated.

Am broke down by Allison dist right now. 3rd trans in 20k

[Cat568]

Had fluid change 3k ago. No trouble. No codes. Burnt up. Allison and I are insane about this. They are trying to blame monaco or Cummins. Hey, no one knows what the heck. Just got it on fri though.
Managment is involved.