Your question is somewhat difficult to answer with 100% certainty because of the unpredictability of US domestic airlines requiring that passengers place their baggage in a sizer. I've never had to do it, and a lot of sizers in US airports appear to be gathering dust, but there are occasional reports here at FT that an airline does it at a specific airport for a day or two and then stops. So long as GAs eyeball your bag (if they even pay attention), you're not so far over the limit that you're likely to have to check your bag other than when the overheads are so full that you'd have to gate check anyway.
Another complicating factor: a similar inconsistency with international carriers that appears based on how much in fees they want to generate from baggage. The big carriers, like BA, seem to have a similar approach to US domestic airlines since I've never really seen them consistently force passengers to use sizers. Airlines like RyanAir, on the other hand, make up a lot of money lost from their low-fare tickets on baggage so they're measuring and weighing in an intense effort to increase the airline's profit. Throw in some other airlines where there are even more stringent restrictions on size and weight to begin with, and you may find that a bag that would definitely meet size and weight requirements here may not there.
Given that funds are a little tight right now, I wouldn't run right out and buy another bag just to trim a couple of inches. I would think about maximizing any "personal item" you might carry--even a rapacious carrier like Spirit still allows a free personal item. I try to pack mine so that I have one change of clothes and my toiletries in case what I thought was going to be a carryon becomes a checked bag that then becomes a lost, checked bag (don't laugh, Southwest once lost a checked bag on a nonstop flight from MCO to ORF where I was in the terminal two-and-a-half hours early).
I might also keep in mind that airlines are probably going to increase their vigilance about these issues and be on the lookout for appropriate bags when you do eventually decide to replace your current bag.