transmission not getting 5th gear

When you say 'the car stalls' I think that you mean that the engine quits. That does not sound like a transmission problem, I don't think. If you mean that it doesn't shift into top gear, that's not 'stalling' but it could be a transmission problem. I'd get a second opinion. Yes, a transmission could cost $4k but I'd go to a transmission shop for a diagnosis and estimate first. Here's a directory link for you: https://repairpal.com/infiniti-repair-in-columbus-georgia