Q: Delayed engagement on the drive selection.

My car has a delayed transmission engagement on drive it takes 2+ seconds sometimes to catch the gear, it gets even worst when the car is hot, when is gets to running temperature it might take 4+ seconds to engage drive and the delay might even relocate to the reverse gear too, the fluid is pretty new (reddish) and at the right level, the previous owner told me that the car will overheat sometimes due to a bad radiator and had a misfire, I replaced the radiator, I replaced the plugs which caused the misfire and the overheating went away but still has a delayed engagement, I'm planning on changing the filter just in case, even though I don't hear any high pitch noise coming from the tranny or any other noise or sounds, when driving it doens't slip or shudders it works fine, it doesn't leak either, any advice on what I should do I've already spent a ton of money in the car, I can't afford aamco or a tranny shop, Any advice????

My car has 160000 miles.
My car has an automatic transmission.