As ScottG said you will notice the difference in diameter especially if you are running the 3:42 gears.
If yours is diesel I think the 3:42's were all that was available except for the DRW 3500's. You effective ratio with 295's will drop to 3:31 (new diameter/old diameter x ratio). For it to remain same your gears would need to be changed to 3:53 which would surely not be worth it for the cost involved. Whether "you" will be ok with it or not only you could say unfortunately it would be after the fact. There is probably a calculator out there somewhere that could tell you what your rpms would be with that new ratio that might help in that decision beforehand. Around town may not be too noticeable but once hooked up and towing in the mountains you will notice it but again you may be fine with it and then again you may not, heavier the trailer the more pronounced it will seem .
Your speedometer should be able to be re calibrated but if not it would actually be just over 2mph faster than the 275's and what it shows on the speedometer.
