Lets start from the beginning. You were towing a trailer on a hot day and the trans started venting fluid. The fluid is grey and nasty, thats most likely why the fluid is overheating and venting. It could be contaminated by engine coolant. You have a check engine light on and a flashing O/D light, has a scanner been put on it to determine why the lights are on and flashing?? What are the codes being set?? The vehicle is going forward in all gears. That is an indication that severe overheating has caused the forward clutch pack to weld itself together. Your transmission is totally destroyed. Dont bother trying to just replace the converter, that would be a waste of your time. Before replacing it, you really need to know why it went and fix that problem so your next transmission doesnt meet the same fate. Look into the cooler and also install an external cooler for extra protection.
transman