1989 Ford Mustang smoke and not shifting

My cars' transmission was rebuilt last year, and has been peachy since. Four days ago I went into the mountains and did a mile on a dirt road(making her feel like she was shaking apart, need new shocks in the rear). The next day I take her to the mountains again, and she starts smoking coming back home. White smoke and bad smelling. It was pretty bad. A few people passed me to get away from the smoke. I got her home and let her sit over night. I checked the fluids in the morning and all of her fluids were topped and there was no antifreeze in the oil. Let her sit for another day and took her out today, she started smoking again and now she won't shift. Took her to my repair shop and they think its the transmission or the gear shaft? Which they said was moving around with a lot of play when they checked it. What could be the cause of this? And if it is the gear shift, would that be covered under their warranty for the transmission? I paid 2800 last year for the rebuild and I am praying its covered but would like a better understanding of what the problem is so that I can talk them down in price if it isn't. Thank you for all your help!