Have Any Frac Sand Haulers had an issue like this? (My worst fear has been realized)

I remember watching an episode of House with another driver about 4 years ago when I was barely coming out of trucking school. House always seems to have a patient who comes in and the doctors seemingly can't figure out what is wrong with them because they have this extremely rare condition and house figures it out at the last minute what is wrong by chance and saves the day.

We joked about the fact what if you get a truck and something goes wrong with it and the mechanics at the main dealerships just can't figure out what is wrong with it for their life. Do you find yourself going to multiple dealerships or shops getting multiple opinions until a genius mechanic comes across what the actual problem by chance? Well, My worst fear has been realized and I have officially signed up for truckers report after 4 years as an owner operator to see if any other frac sand haulers have had a similar issue as mine.
I have my truck here at a freightliner dealership in Texas and have had already had 5 mechanics in the oilfield look at it prior to me bringing it to the dealership. The mechanic at the freightliner is stumped out of his mind now and I am officially starting to get concerned. That my truck has the rare condition know one knows how to fix.

So here is the issue.
For those of you that haul frac sand you understand you have a PTO and that you have to turn the PTO on when unloading and crank the cruise control up to about 1100 to 1200 RPMs to blow off sand.
(I have a 2016 cascadia so it uses a bypass switch system and I pump off at 1100 rpm).
The pneumatic trailer will reach up to about 1200 to 1500 PSI before I open up one valve on one silo and blow off one silo at a time. Well basically it doesn't take long for the PTO pressure to get to the truck now and all the sudden its as if it is too much for the truck to handle and the RPMs start to fluctuate down to 800 then back up to 1100 then back and forth. By that time I am clogging and find myself taking alot longer than an hour to pump off. Way longer for a long hose.

We checked it on two different trailers to make sure the check valve on the trailer wasn't the issue.
Checked the electrical connection on the bypass switch to make sure the high vibrations weren't causing it to have a loose connection. And as of today we have hooked up a computer while its having the issue and no codes show up and the computer doesn't show any issues with the truck. I was hoping it was just a sensor issue but that seems to not be the case anymore.
The blower is still blowing and the mechanic that installed the blower is convinced that it is something to do with the truck while freightliner mechanic is potentially starting to veer towards an argument that something is wrong with the blower. I am in a spot now where if no one can figure out this issue i have to hang up my hat with truck when it comes to hauling frac sand and say goodbye to my last ten months with this blower and the $9000 i have spent on this blower and go do something else with my truck. The cruise also works just fine at 1500 rpms while driving. No weird slow down in the RPM.

If anybody has ever had an issue like this It would help me greatly if you could help me. I am also open to all suggestions on things to try or look at that I may have potentially missed.

I have been pumping off for 10 months now with no issues like this. preventative Maintenance performed on blower every 6 months by the shop that installed it. Also there is no leaks on the blower and the heat plug is still intact.

 

It can have this issue when the tank is completely empty as well and just airing up.
Thank you for the advise as far as the bearing that is something i will present tomorrow to the mechanic and see if they can check it. Thank you. I am literally open to all ideas of what it could potentially be.

 

1500 is a bit high. for the most part i'll unload at around 1200 psi. It is a paragon blower. I have been using it for 10 months unloading at the same PSI and it hasn't had any issues like this.

 

I have run the PTO without it connected. It does just fine and doesn't have the issue at all. Which implies when the pressure from pushing the sand is involved it starts stopping it up.