I also sent you a PM if you are are looking for a caravan to get your there, I am wagon master on one crossing Jan 11th, but from Az. They will do a one way to Chapala. That trip going the whole way crosses back at Laredo. The NE is less safe than the Nogales crossing, especially for a newbie, and getting a 5th wheel around Guadalajara if you are not familiar with that area can be a challenge. Another alternative is to see if you can tag onto Pierre Blais caravan (amigos Rodantes)for 2 days, which is predominantly French, but he crosses in east Texas(Hidalgo). He can get you close and at least across the border. He crosses on jan 7 and if he follows the usual pattern ends up within striking distance of Chapala. I may also be presenting seminars at the RV show in Toronto in mid October if timing is correct, and you can get a lot of info on driving in Mexico from me. The only route I would probably consider from the east is the columbia crossing at Laredo. if you have read the other thread you will see the problems with some Texas crossings and 3/4 & 1 ton pickups, but we hope to get that resolved by January. If this is your first trip, you may want to find others to travel with or use a commercial caravan. That partially depends on if you want to see some stuff like Copper Canyon and some colonial cities enroute or you just want to get there ASAP. You never said why you want to go to Chapala. There is no RV park there, the closest is Roca Azul & Villa Corona.
The other factor is your truck. Is it a post mid 2007 deisel? If so ULSD is still not availble in Mexio and you may want to take the shortest, most direct route in that case, which means Columbia. Just be aware that that route takes you through a lot more remote countryside & boring, so plan your stop well. It's a 2 day trip.