tb isnt bad, just a few bolts. watch though, a little coolant will come out when it comes off. 150k is right around the time for the cats to go bad, tho u most likely didnt change the cat when you did the engine, so it is probably pretty old. but i dont know if that would cause surging. front o2 can cause this i think. also, try running the car with your maf sensor unplugged and see if theres a difference.