I have a '95 T100 SR5 4X4 with 82,000 on it and recently have had a starting problem.. When I start the engine, it takes several cranks and then turns over.. When I look out the passenger side mirror, I see a puff of black smoke when it finally starts.. I took it to a Toyota mechanic and he thought it was a problem with the plugs because they were well worn so he changed them with Toyota plugs and plug wires.. He was going to change the O2 sensor but wanted to replace the plugs to see if that would solve the problem.. Well, it didn't.. It's a big expense to change the O2 sensor.. Would replacing it resolve the starting issue?? Other than starting it up, it runs great! I did run some Lucas treatment in the gas tank and it fired right up every time for 2 tanks now back to the same problem...Got 19 mpg on the last trip with the Lucas in the tank.. Help!!!