I haven't done such a tour, but researched this thoroughly before eventually doing the canal by cruise ship, having thought seriously of doing exactly this.
I had originally been meant to transit on a break-bulker but the company went bust shortly before I was meant to sail.
I had no interest in doing it on one of the international cruise lines, but eventually, after about ten years or so, found a mid size ship with a scheduled day time passage on a UK cruise line, starting at first light at around 6am, passing into the Pacific at a bit after 5pm. That is the normal slow passage time for both cruise and freight ships with a rigid speed limit (no slower, no faster than set limits all the way through). Westbound we passed through in the convoy leaving at first light. I would have to say that we had the most wonderful narration from a live guide, coupled with both an enrichment talk beforehand (on our Transatlantic line passage from London Tilbury) and a movie of the story of the building on the cabin TV's for several days beforehand and afterwards. I can't speak for other lines, but felt I got everything I could possibly get out of the experience. Thus I don't believe a small boat could go any slower, nor do I think it would have given me personally anything more.
This is the only company I eventually came across- https://www.panamacanaltrips.com/
I assume the above tours are doing the Old Canal, as I did, as opposed to the new Panamax one.
I went in January 2020 and got a stunningly good day weather wise. Due to it's location in a rain forest rain is to be expected, as are apparently mosquitoes and other insects. I was heavily covered in bug cream, but the lack of rain (?) meant they never made an appearance that day.
We had the previous afternoon in Colon, with very strong security warnings. A city which has had a very tough time socially and is quite rough and ready. We had a heavy duty briefing on personal safety- and I would advise caution by day and be very careful indeed at night.
I can't tell you about Panama City as we were straight out of the canal for a 9 days Trans Pacific line voyage. The ship's tours ran well late due to the apparently very heavy (but normal) traffic in the city- or so I am told.