I use the right trigger on my controller. Unlike a keyboard where a key is either on or off. On the controller i can control the amount of input. So if i press the trigger 50% down, normally that would result in 50% engine power or speed, just as if you were using a pedal.
How that typically works no matter if it's a rally game, F1 or city driving is that the car will accelerate appropriately and change the gears to match, so if i press the trigger 50% down it might only change gear into 4'th out of 6 gears maintaining cruising speed, behaving like a normal automatic gearbox.
In snowrunner, if i press it 50% down, it'll continue to change through all gears until it hits a gear where it can't maintain the speed and then it'll drop into 1'st, it'll rev the engine even tho i'm not moving the trigger meaning the revs should stay consistent in each gear.
IE. Ford CLT9000 with highway gearbox on asphalt, if i press the trigger 50% down, it will accelerate until it hits 5'th/6'th gear where it'll drop straight into 1'st.
I guess maybe this has changed into a gearbox issue.
Hope this helps clarify what i mean.