Switching to road wheels/tires on a gravel bike

[cycle tramp]

I am looking to do more road cycling this summer so want both options as have already noticed a lot more resistance when out cycling with my friends on 'road' tires.

Are you sure your friends are not just a bit faster than you? Tyres do make a difference of course, probably more than anything else.

As already has been suggested I'd go for a second bike with thinner tyres to see if that makes a difference...
..however..
I'd also like to pick up on PH post... many years ago I used to ride with the Sunday morning road crew... I was always at the back and always struggling, no matter how many performance/ go faster bits I got for the bike..
..anyway one day I lifted my head from my 'areo tuck' (as suggested on pages 16 to 19 in this months edition of performance bicycle (or whatever)) realised that I'd been missing out on great views and gave up cycling with the road crew there after....
..many years later and several bicycle tours later I find out that my lung capacity is much below that of an average person - which may mean I may never had been able to keep up with the Sunday crew no matter how good my bike was.
..I still enjoy cycling but its now on my own terms..