What was found
NR 1 BLEED OVERPRESSURE EICAS MESSAGE, AT ABOUT 5000FT. RAN CHECKLIST AND OVERPRESSURE REMAINED UNTIL IDLE POWER AND LEFT BLEED SYSTEM WAS ISOLATED. RETURNED TO FIELD, NO EMERGENCY DECLARED, LANDED WITHOUT INCIDENT. NR 1 BLEED OVERPRESSURE AGAIN DURING CLIMB WHILE BLEED WAS ALREADY ON MEL. ALSO HAD NR 2 BLEED OVERPRESSURE. RETURNED TO FIELD, NO EMERGENCY DECLARED, LANDED WITHOUT INCIDENT. R & R NR 1 ENGINE SHUTOFF VALVE IAW AMM 36-11-03. OPS CHECKED GOOD. ALSO R & R NR 1 BLEED OVERPRESSURE SWITCH.