I had a G-tech meter and used it on my '89 Jetta.

It said that it had 133 horsepower although it only had 102 Hp stock. G-tech meters are not very reliable in my book as you've found out. It really all depends on how hard you gun it and try to throw yourself back in the seat. I had the Jetta at about 6,000 RPM's in first to get that reading.