Is there any GA acft where VNAV drives VDI successfully en-route?

[tset 2]

Ok, let me take another approach here.   While waiting for the G600/GTN and whatever nav/autopilot integration is available,  is there a way to use the GTN with all the sim navigation and autopilot interactions turned off?  In the Laminar G1000 C172 at least, GPS nav is "broken" when the GTN is active.  Testing in GPS mode, not vor/loc.   I've tried turning everything off in both GTN settings.  Even if only the GTN radio tuning worked,  it would be very valuable.  Can we leave the G1000/GFC700 functions alone until the G600 and still get the other good features of the GTN?

Regards, TS

[tset 2]

Does anyone have a GA aircraft that is running the GTN750 in which en route vnav is driving any vertical deviation indicator successfully?  And, while I'm dreaming, will your autopilot fly the descents?

Regards, TS