Crossroads in My Career

An asistant manager from Engineering Department asked me last week if I was interested to be a Product Engineer. I asked him 'Why?'

He mentioned that he saw me doing my job well that includes stepping into technical details and co-ordinating among departments. When he found out that I was from engineering background, he told me to let him know anytime I would like a switch in my career.

His offer really made me think hard. Should I go back to a career involving technical requirements again? If this is really what I have wanted, I should have stayed to be a QA Engineer 2 to 3 years back and I would be in senior position by now. If I make a career change, have I wasted 2 years in Business Unit department in my current company?

I am trying to analyse the reason why I would even consider this.
1) I was not given an upgrade/ promotion during my last performance appraisal although my superior has been recommending but it was disapproved by top management
2) I just found out the salary increment/ promotions for executive level is far too low/ slow as compared to engineers
3) Being a Product Engineer is also a right career path to achive my goal in my career. It is more high profile and noticeable to top management so reason no. 1 will not happen

However, I like the job I am doing now but am I under-achieving? Although I am very busy in my work that requires for me to stay back until 7:00pm some days, can this be done by anyone else? Is my job easily replaceable?

If I stay at my current job, how soon can I reach my goal?
If I switch to engineering department, will I have to start from scratch again in terms of positions and grades but will this allow me to get promoted faster?

Nothing is decided, I will just wait for another performance appraisal end of this year and see how it goes.