Sorry, I've been busy.
There is definitely a restriction in airflow somewhere upstream of the intercooler. Sometimes the hot side of the intercooler gets full of goo. You can look inside with a mirror.
It could be that the air filter is super clogged.
One of the first things I'd look at is the turbo. Between 2008-2010, the turbos were honestly not very good and sometimes they just don't spin. Give the compressor wheel a spin and see if there's any binding. If there is, replace the turbo.
Thanks for the reply.
I pulled the turbo hose and it spins freely and no play. Although I did notice a bit of oil on the hose.
I don't know if it's a silly test but I swapped the intercooler with another exact same truck (truck 2) and it works well on that one, and the issue continues on truck 1. As I reassembled everything back on the 2 trucks I got curious and checked the amount of air coming out of the turbo hose, truck 1 turbo spins and blows air but not even close to the pressure of air on truck 2. I reconnected the turbo hose on intercooler of both trucks and removed the outlet hose from the intercooler to compare amount of air coming out of the intercooler and again on truck 1 only feels a little bit of air pressure blowing out and turbo sound it's quite less than on truck 2 (truck 2 almost blows your hand away ).
I had a load on the truck going like 7 miles away from our yard so I decided to drive it with the intercooler outlet hose disconnected (was not the best but needed to avoid a claim on the load) and the truck felt good although obviously without the turbo boost wouldn't go over 50mph and struggled on a little hill on the way.
When I was delivering (after the 7 mile drive) I heard the turbo sound increased, I popped the hood and checked on the outlet side of intercooler and was blowing hard as truck 2! Connected the hose back and the hose didn't compressed and truck felt as it's supposed to. But when I got on the highway once I hit 64-65mph I heard the turbo sound decrease and check engine light came on. Read code P0087 ( fuel rail/system pressure - too low bank 1)
Don't even know if both things are related but I will check for clogged fuel lines today (as you recommended on another thread about this code) and will take it back for a ride and see what happens.
I'll update in the afternoon, any ideas are much appreciated