Hi guys, new here, first post and it might be a long one.
TL;DR I need a good mechanic around the Barrie area who knows what they're doing.

So I have a 2006 V6...GT? I never know what to call it lol. The car started off as a 2006 4L V6 but after about 64K I was eager to get some mods done. I was very new to the whole car scene (even more so, the car modifying scene) so after some quick research online I found that getting a supercharger would the V6 would mean topping out at 350ish hp. For the same kind of money I could swap out the motor from a GT which already sits at 300 and work my way from there. For the long term goal of going somewhere near 500/550 whp this obviously seemed like a better solution. Anyway, I got a motor/tranny/rear end from two different 07 and 08 GTs, and went to work. I had a shop in Brampton (where I lived way back when I got this done) and the job was done well. The car drove perfectly and between 2008 and last year the only problems that came across was a blown AC compressor and a broken alternator wire. Now the car is sitting at 142K and one very annoying issue has come up. In stop and go traffic (almost always on hot days) the car starts to surge abruptly before idling rough. The codes that pop up are always pointing to the throttle actuator control (stuck) or throttle sensor/position switch circuit voltage issue. I bought a new TPS and replaced it. Car was fine for a little but the problem came back. This time I took it to Ford in Barrie and they ran a diagnostic...nothing, had the car for a week, drove it to empty tank and nothing. I parked the car away after cause it was close to snow season now. This year I took the car back out in late February early March and the car was perfectly fine until yesterday...same thing. Was driving along Highway 27 and the car forced idle. No response from the throttle pedal, nothing. So I'm kind of stuck...its the exact same symptoms every time so...yeah...
Edit: After the engine swap I stopped modding all together...could only afford school or car mods so school took precedent but I'm done now and would like to finally finish what I started all those years ago...