Recheck the output shaft seal between the booster and master cylinder. If it may have been compromised when you replaced the MC.
Bleed the brake system starting with the shortest link and working outward progressively to the longest. Bleeding the longest path first may leave bubbles in the system.
Pressure bleeding the system is prefered to prevent sucking air into the system.
A very good and inexpensive way to bleed brakes is this: Get a 20-foot length of 3/16" tygon tubing and an adapter for one end of the tubing that will fit onto a bleeder port. Connect the adapter to a bleeder port and open the port about 1/2 turn. Run the tygon tubing around the truck and past the driver's door so the fluid running through the tubing can be seen. Run the open end of the tubing into a suitable can to catch the fluid. Fill the master cylinder reservoir with new fluid, leave the cap off then begin pumping the brake pedal slowly and firmly about three-quarters of its stroke. The brake fluid will be pumped out of the bleeder port, down the tubing and the run-off collected in the can. Keep pumping slowly but firmly until all the bubbles in the tubing are cleared and all the old fluid pumped out. Keep the master cylinder reservoir full as you go along. Close the bleeder port and proceed to the next one.