GPS Issue - Help needed please!

Hi

I'm hoping for some clues as to what to do to sort a GPS issue.

I upgraded my coloumbus from V3 maps to V7 maps last week. All worked fine except didn't have full postcode entry. After about 3 days I noticed the position indicator on the map was occasionally going off course. Figured that as I didn't have full postcode entry option either I needed to upgrade the firmware.

Upgraded this to Version 2764 on Sunday courtesy of a local forum member (thanks Ray!) reloaded the V7 maps and all seemed well.

After a while had the same positional problem. Tried sytem reset <>i and then also left it overnight and tried again in the morning. GPS took over an hour of driving to finally find satellites and get a fix.

Reloaded the V3 maps to see if it was a dodgy map disc I had. Worked at first then went off course again. Left overnight and on same route to work took 40 mins to get a fix.

Reloaded V7 maps again having ruled out dodgy disc issue. Got a fix after an hour this morning. This evening no fix after a 2 hour drive.

Totally stumped.

Can't be the firmware as problem existed before

Can't be the map disc as tried both and same issue with both

Can only think that the antenna has developed a fault and its coincided with me changing maps? Unlucky or what?

Any ideas anyone or is there a way to recalibrate the GPS??

Please help as I'm lost at work without Sat nav.

Thanks

Andy