Very slow once connected to GPS

[daq]

I have Eten G500 with built in Sirf III. It came with Navigon Mobile Navigator 5 preinstalled. I've read so much about TT that I finally decided to get TT6. Now the problem: when I just start the program without GPS receiver being set up it works nice and fast. Then i select other receiver, and as soon as it connects to the GPS receiver I get MAJOR lag. There is probably 5 seconds pause between a tap on the screen and menu appearing. Navigation works OK, but entering the address takes 5 mins because response to buttons is so slow. I tried searching for this on line, but could not find any solutions.
I'm also waiting for response from TT, if they respond with a working solution I will post it here.

Any suggestions welcome.