Regarding the throttle plate closing up top; There are a couple of options around $400. They are a tps modifier device offered by blitz and buddy club. The problem is that they make the vehicle a lot less predictable and glitchy at partial throttle conditions from what users report.

Another option would be a stand alone ECU like AEM EMS or if you have the money to spend, then Haltech, Motec, Hydra or Autronics which can control drive by wire.

It basically depends on the customers needs and size of the wallet wether it's an issue worth addressing or not.