GRDMITRO... 3500rpm to 5000rpm through gears on steep uphill works well for my 1.2 GE. Its powerband is in that area. Fall below those revs and it can feel breathless. For a GD, torque builds and peaks at lower revs, however... I think.
DOWNHILL I use my lower gears a lot for engine braking. Rather than 'whack it down' the gearbox, I brake momentarily as I change down which, I hope, eases mechanical stress through the transmission. Smooth braking timed with the (gentle) downchange also helps maintain overall balance of the car and so, I hope, helps maintain grip on all four tyres. (Brakes discs and pads are more expensive to maintain in these post-asbestos pads days.) However I then will use the brakes a little to stop it revving its head off... first gear engine brake if necessary, too. Lorry driving years ago with heavy, unstable loads taught me these habits - whether they are good or not so good. And lots of fast driving on gravel roads.
Apologies... having posted I realised yours is a GD. However the gist of it must be about the same, I think.