3406e boost issue

Hi y'all. I have a 96 FLD with 5ek cat engine. Its a 375 rated engine. I have a boost issue. With a KR scan gauge, I only have 18 pounds boost. i replaced the boost switch and still have no boost. I chequed the CAC, no serious leaks. the horsepower on the scan gauge shows 285 max. I replaced another turbo but it was a 3126 cat engine turbo. It only made 6 lbs boost. No black around the exhaust manifold. I cant build boost in any gear.
Bad turbo? fuel supply issue? Took it to 4 shops, nobody has an idea. They just wanna throw parts at it. I thought a turbo worked or it didnt. The wastegate never opened on my turbo or the other one. frustrated , going broke and wanting to learn and understand. I haul 40k of crude. I have not been able to hit 55mph loaded on the flat.

 

thanks for the suggestions. have replaced the boost switch Cat shows it , Fliner doesnt,It just shows the boost pressure on the 5ek. Later models are a boost ambient combo switch i have been told. I also changed the charge air cooler, all boots and clamps. I dont have cruise working yet, again. they just wanna throw parts instead of fixing it. I borrowed a buddies cat computer, I shut down one cylinder at a time and found 1 cylinder no change. Very little change on another cylinder. I replaced both injectors and it runs much better. I never thought about the fuel filtre. I will replace it tomorrow. I found a guy to change the settings on my ecm and take out the factory derates. WHAT A DIFFERENCE! That in itself made more difference than even replacing both bad injectors. I cleaned the air filre and am ordering the fleet air filtre from pittsburg power. Tomorrow i am gonna load crude and see how she does. I think Im gonna name her patience. it sure is trying to teach me some....

 

it ended up being 2 bad injectors. Much better now. Thanks everyone!