WE HAVE A 2000 F-650 WITH A CAT 3126 MOUNTED WITH A CHALLENGER 21 FT. STEEL BED. IT IS ALSO A EXTENDED CAB. WE HAVE HAD PROBLEM WITH THE TRANS & CLUTCH SINCE DAY ONE THE HYDRO PART OF THE CLUTCH GOES OUT ALMOST ONCE A MONTH. IT HAS HAD 13 CLUTCH MASTER & SLAVE ASSEMBLIES AND THE TRUCK WILL BE TWO YEARS OLD IN SEPTEMBER. FORD SEEMS TO HAVE NO CURE FOR THIS. THEY HAVE REPLACED THE FLYWHEEL,PRESSURE PLATE, DISC, RELEASE BEARING AND STILL THE SAME PROBLEM. ALSO THE THE TRANS HAS BEEN REBUILT THREE TIMES AND IS STILL VERY NOISY (HAS A 7 SPEED SPICER TRANS). THE REAR MAIN SEAL IN THE ENGINE HAS BEEN REPLACED TWICE AND IS LEAKING AGAIN. THE COOLANT TANK CRACKED THREE WEEKS AGO AND IT TOOK TWO WEEKS TO GET ONE! THEY CAN'T SEEM TO GET THE FRONT END RIGHT EITHER HAS BEEN ALIGNED 4 TIMES AND IT STILL EATS FRONT TIRES IT'S READY FOR THE THIRD SET AND IT JUST TURNED 80,000. WE LIKE THE SIZE AND FUNCTION OF THE TRUCK BUT MAY HAVE TO GET RID OF IT CAN'T STAND THE COST OF REPAIRS! ANYBODY ELSE HAVING PROBLEMS WITH ONE OF THESE TRUCKS? AND IF YOUR THINKING OF BUYING ONE BE CAREFUL YOU MIGHT HAVE THE HEADACHES WE ARE HAVING.
Check out www.ford-diesel.com , the forum has a section for F-650 & larger trucks , you might find some answers there.
THANKS FOR THE LINK I DIDN'T FIND ANY ANSWERS BUT I MADE A POST SO MAYBE SOMETHING WILL COME UP.
We are looking for a new F-650 but will look into Fords problems before ordering, Thank you.....
Compeditor had a clutch problem with one of their F650's. How about the automatic trans?
AUTOMATIC TRANS IS ALLISON SHOULD BE FINE THEY HAVE BEEN AROUND FOR A LONG TIME BUT WITH THE AUTO I WOULD GET THE MAX. HORSEPOWER OFFERED!
Thanks for the info... will work with what Boss decides and deal with whatever he wants.
Fords are slow pigs with tractor motors, no pick up, we are wrecker operators. We need power & Quikness. Tractor egines are for the farm not the interstate brother!
Look at the Chevy / GMC C5500 0-100 in seconds double hooked handles like a luxury car. But you'll need a pilots license to fly one. 
The company that I drive for has 4 01' chevy 6500 with the 3126 Cat and auto allison trans. they work well and we have had zero problems. As for the issue with cat parts, we have a branch here in town, so i have never had any issues.