Harder shifting when cold isn't unheard of; the ECU (or TCM, if you have an '05 and up) increases line pressure when the trans is not yet up to operating temperature. The worse situation is when the trans fluid gets overly hot; shifts will get *really* firm, then.
Anyway, if you don't know *any* maintenance history, some people say "leave it as-is", with that mileage. Not to scare you, but you're about at the mileage where the 4L60e in our trucks give their last, and need repair / rebuild / replacement (take your pick). If it does go out at some future point, figure that you got your money's worth out of the OEM / stock trans.
Since you're saying that the fluid doesn't smell sweet / look pink, I don't see the harm in doing a pan drop / filter change / refill w/ 5qts of new fluid.
If you want to do a more thorough job with fluid replacement, you can do a fluid replacement yourself. You'll need about 15-16 quarts of fluid, and you'll be letting the car pump out 1-2 quarts of fluid, then shutting it off and replacing that same amount. Do it after the pan drop / filter change / fluid refill, as that'll be 5 less quarts you need to worry about, and wastes the least amount of fluid. I used a gallon jug with each quart marked off / dashed line across the outside, so I could see it from the driver's seat and turn the key off, each time. And I think I have a post somewhere on this site on how I did this, in detail. There are also other threads by people here showing how they did it, as well. Take a look.
The thing you *don't* want to do is have a machine 'reverse flush' the trans, or add some sort of cleaning solution to their machine. Those are the things that dislodge the small pieces of wear items that have been collecting in the trans, and would be in a 'safe' spot, except for the flushing machine coming along and moving them around into places where they harm the functionality of the unit. That's also when you wind up doing a rebuild or replacement on them.
There are places that don't use 'reverse' flushing; they can be OK to use, if you're not a DIY kind of guy. Most of us here do it ourselves. If you have an assistant, it's pretty much child's play, but you *can* do it on your own - I did, using the method I mentioned, above. Besides the gallon jug, you'll also want some clear tubing, so you can see when the fluid starts running clear.
If you want to really get fancy / be fastidious, you can get the fitting adapter that's used for installing external trans coolers, fasten it to the upper outlet in the radiator, connect it to the tubing, and you're all set (it's also a safer way, if you're doing it all by yourself.)
One last thing - depending on the year of your truck, it may specify Dexron III as the replacement. Use Dexron VI, instead; it's backward-compatible, and GM specifies it for vehicles that were running the older spec. It's hard to find Dex III anymore, anyway (although I do have one place around here that still sells it).