It will not necessarily look bad that you took five years to complete your graduate degree. Admissions committees understand that you are working full-time and will only have a limited amount of time to devote to your studies.
A very good graduate GPA will help offset a lower undergraduate GPA, but only to a certain extent. This "extent is really up to how much leniency the admissions committee chairs to extend to you. The amount of leniency they will extend is primarily based on compensating factors such as a solid graduate GPA and excellent GMAT performance, but it also relies substantially on other factors. These factors include your "likability factor. Basically if the admissions committee likes you based on the stories you tell and the insight you have gained from your experiences they will extend to you and even greater deference than just simply a great GMAT score and solid graduate GPA. You have to make them like you through what you have to say -- that is the bottom line.
The important thing to remember is that you will be competing against a number of other candidates who on paper look incredibly similar to you -- except for the fact they will not have had performance issues at their undergraduate institution. So while it is a about you versus the admissions committee, to a greater extent it is really about you versus your applicant subgroup. Put yourself in the shoes of the admissions committee if they have 10 other candidates just like you why should they give that last spot to you? This is why the essays are so critically important in the essays I believe, in your case, will be your saving grace.
So what can you at this point? You really need to explain your undergraduate performance in the optional essay -- of course. But really, the only excuse for lower grades as an undergraduate is based on valid competing interests. So if you have to work full-time in support of your studies because you come from a socio-economically disadvantaged background, then that could be a legitimate excuse. If you have something acute happen to you, such as a severe illness (you or someone in your family), then that could also serve as a legitimate excuse. Just make sure that you explain the circumstances and do not beg or plead with the admissions committee. Do not let them figure out what happened, but let them draw their own conclusions.
another point that I wanted to address, your seven years of work experience does help and weighting your GPA slightly less, but it is not enough to turn your 2.88 into a 3.88.
I hope this helps.
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