ThomZe, you need the great program that Drew MacPherson created for comparing transaxles and tires to determine your speed/RPM for any gear. I don't remember where I downloaded it from but PM me your email address and I'll send you a copy. It has control files that you can use to add different wheel sizes or VW trans gear ratios so you can determine what your RPM in any gear at any given MPH or KPH. Also, there are some cool spreadsheets out there that do the same thing, you just have to Google around for them.
Greg
could be lack of timing advance, as TDI's like their advance! do you have an intercooler on it? is it a true TDI converted to mTDI or a 1.9TD converted to mTDI? could be injectors as well... but like jimfoo said an EGT gauge would be a good investment unless you don't mind big problems later on...
forgot to answer you! it's a AHU\1Z engine, I've posted the picture of it before, but it's showd here again:
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