Because you were able to substitute the MAF for another as a test, can you also exchange the MAP to see if any difference. I don't suspect the MAP as being the issue since it would be all the time. They are usually reliable. Most electronic items which are sus, are nearly always worse when hot and ok when cold IF they display a problem. The only heat the MAP gets is from the compressor action of the turbo heating the incoming air above ambient. With a front intercooler the air hitting passing the MAP should be fairly cool, but a bit above ambient. What is the intake manifold like? is it gunged up with a black goo coating inside. If so the EGR may be sticky but should also create a code if so. Is the throttle butterfly free and unrestricted?