Help with Mazda 6 automatic gear box problem

[Jack D]

Please can anyone advise, my automatic 2l Mazda 6 08 has a gearbox problem, after driving for a while in queuing traffic go stop go stop go stop... This problems arises i accelerate but it doesn't automatically change up to second gear it's stays in first for much longer than is normal and just when you think it's never going to change gear with a bit of a jolt it will then change into second at a high ish rev - I get the impression that it does this when the engine / gearbox is hot I have looked at the gear box oil level and it is correct. So, can anybody advise maybe the problem are their any electrical sensors or something like this that could be faulty? or is it a mechanical issue? Any advice would be fantastic. Thank you very much.

[Sardonicus]

I would imagine the box is due a good service (fresh oil and filter/strainer) so often missed with auto trans until they show problems hanging/lazy/slow gear changes is one of them