Hy Curtis65, welcome, I don't often get the chance to say this but your truck is too new and too small to fit into my area of expertise. I think your decoding of the serial is accurate
4, year, have to look at body style to confirm
K, GM code letter for four wheel drive
9, Canadian identification number for GMC truck
250, Canadian designation for a 3/4 ton truck
The balance of the number is the regular production number
B, is the weight class (GVW), with A being for a 1/2 ton, B for a 3/4 ton etc., hope that helps.