I would start with the 4-wheel alignment. Who sold you that? It's not possible since the rear is not adjustable. Makes me think a monkey did it and it ain't right. Post a scan of the print out you got with the alignment. I'll tell you if it's right. No print out? A monkey DID do it then.

Brake hoses are common pull causes on the GMT400 trucks. With no pressure on the pedal, open the bleeder on the RF. If it spurts (yes, I wrote that), suspect front hoses. If not, keep looking.

Not sure what you mean by "Within a year the idler arm will be shot"....are you predicting the future or did you mess up your tenses and you had a more rapid than expected failure of the idler arm? Idler arms are JUNK on the 400 and don't last long. There is a chance you bought one for the wrong application (at the fault of the parts guy) that has an improper amount of drop, offset, etc. This type of fouled angularity would wear parts and cause a pull most likely.