A major downfall with current drag cars in the game is the lack of manualised automatic transmissions. of course, you could give them a PRND1234 layout, but this isn't really appropriate for cars where shifting from 1st to 2nd is crucial. I think a good way of getting around this, while adding an extra layer of customisation, is to have the control valve body as a selectable part under the transmission. that way, you could have a more short-shifting prone factory setup for larger engines or economy applications, and you could also have full manualising conversions, which overwrite the automaticmodes to PRN1234, without needing an entirely separate transmission.
The CJD Special Tunes mod has valve bodies like this, not sure if they work like you described though, I don't use them
They have manual valve body automatics in the crawlers and offroad racers iirc. A manual valve body is something I've wanted in BeamNG for a while now, just never thought to mention it.
With the way transmissions are made in jbeam currently, it might actually be doable to add a "valving" part for all automatic transmissions, that just tells the transmission what shift pattern to use. There's a line called "automaticModes", which looks like these in the case of the hopper's 4A and race transmissions, respectively: "automaticModes":"PRND21", "automaticModes":"PRNM", That line is just a general "vehicleController" setting (vehicleController is the lua controller that handles the standard driving input stuff), so you could put the previous lines in a separate part and it would very probably still work. I'll try it out this evening. Edit: For some more suggestions to the devs on that topic, you could probably make those parts "common" parts, have slots for "auto_trans_valving_3A", "auto_trans_valving_4A", etc, with an option for standard valving (PRNDL) or manual valving (PRNM) for each of those slots.
I just tested it and it works. No need to do it yourself, here's the file: (The transmission is marked as the valvebody one)
The Celtia's 2-speed Auto, found in the burnout config, uses the PRNM setup allowing the player to reach wheelspeeds that essentially glitch out jbeam and stop the smoke altogether... just sayin'