I DID install my air filter gauge that connects to the air tube pre turbo. I also put the old filter in and after starting the bus and running, it showed good air flow. I removed it and installed the new filter and it measured the same! I was hoping for a significant difference but looks like I will look further for what MAY be problem and what may not be!
I am sure you meant the following but just to make sure that
after starting the bus and running, it showed good air flow
....was during acceleration and high speed driving (70s)
Make sure there is no leaks in the pre exhaust turbo pipe as well intake air after turbo to cylinder head.
Otherwise...sound like the turbo is not up to par.
Sojourn for Christ, Gerald