surge at low rpm

Check fuel pressure, throttle position sensor, check the pug wires, cap, rotor etc. On this truck you can pull the code with a paper clip bridging terminals A&B. ( the upper RH 2 terminals in the data link connector under the dash ) with the key on, it will flash the codes. The look them up on RepairPal. A Throttle Position Sensor code will commonly be a 22 plus or minus 1 depending on the type of fault. Just because this truck was made in Canada, does not mean the parts are obscure, many GM trucks were made in Canada, the VIN will begin with a 2. The USA parts usually fit just fine, because the trucks were made for the USA market, even Canadian Market trucks are very, very close to USA Market trucks. One more thing, are you sure the fuel quality is good and does not contain any water?