ALTDEV ALT EXCURSION.

Narrative

PF WAS HIRE PLT PERFORMING MAINT ACCEPTANCE CHKS AS PART OF PRE-PURCHASE. TOTAL FAILURE OF ELECTRIC STABILIZER TRIM (NORMAL AND EMER) CAUSED CONFUSION AND ALARM AND WHILE TROUBLESHOOTING THE PROB; ALLOWED THE ACFT TO DSND TO APPROX 23500 FT FROM ASSIGNED ALT OF 24000 FT. CTL PRESSURES ON THE YOKE WERE HVY AND CONTRIBUTED TO THE ALT 'BUST.' I TOOK CTL OF THE ACFT AND REPLACED THE HIRE PLT WITH THE REGULAR SIC. ATC WAS ADVISED OF OUR TRIM PROB AND ASKED FOR CLRNC TO RETURN TO DALLAS LOVE FIELD. NO SPECIAL HANDLING WAS REQUESTED OTHER THAN A MORE GRADUAL DSCNT PROFILE THAN NORMAL TO KEEP AIRSPD AND CTL PRESSURES TO A MINIMUM. A DSCNT CLRNC TO 11000 FT WAS RECEIVED; FOLLOWED BY A CLRNC TO DSND FURTHER TO 5000 FT. THE 5000 FT CLRNC WAS PERCEIVED TO BE ACCOMMODATING OUR REQUEST FOR AN EARLY AND GRADUAL DSCNT PROFILE. ALL CLRNCS WERE READ BACK. FREQ CHANGE AND RPTING WE WERE DSNDING TO 5000 FT WAS MET WITH CONFUSION BY NEW CTLR WHO INSTRUCTED US TO RETURN TO PREVIOUS FREQ. WHEN DOING SO; PREVIOUS CTLR QUESTIONED OUR ASSIGNED ALT WHICH LED ME TO BELIEVE HE WAS NOT AWARE OF THE 5000 FT CLRNC PREVIOUSLY ISSUED.