FLC OF A B757-200 OVERSHOT ASSIGNED ALT DURING SID CLB DUE TO MOMENTARILY LOSING ACFT PITCH AND THRUST CTL DUE TO SUDDEN UNEXPLAINED AUTOTHROTTLE INCREASE IN PWR. THE CAPT WAS ABLE TO RETURN TO ASSIGNED ALT AFTER STOPPING THE CLB 800 FT ABOVE DESIRED ALT.

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AFTER DEPARTING EFD (ELLINGTON) ON RWY 17R; WITH AN ASSIGNED HDG OF 040 DEGS AND AN ALT OF 2000 FT; THE INITIAL CLBOUT WAS NORMAL AS PER COMPANY PROCS FOR LNAV AND VNAV NAV. UPON REACHING 040 DEG HDG; A FURTHER L TURN TO 360 DEGS WAS ASSIGNED WITH A CLB TO 3000 FT. IT WAS THE CAPT'S LEG (PF) AND HE WAS FLYING THE FLT DIRECTOR AND USING AUTOTHROTTLES. WITHOUT ANY ABNORMAL INDICATION; THE AUTOTHROTTLES COMMANDED AN INCREASE IN PWR RESULTING IN AN INCREASE IN AIRSPD AND PITCH. THE CAPT AND I WERE TRYING TO FIGURE OUT THE REASON FOR THE DRAMATIC PITCH INCREASE (AND PWR INCREASE). I CALLED AN ALT WARNING OF 2800 FT AS I SAW THE ACFT RAPIDLY ACHING 3000 FT. THE INCREASE OF PWR WAS SUCH THAT THE PITCH INCREASED TO A POINT TO GIVE THE ACFT A 2000-2500 FPM RATE OF CLB. AT 3000 FT THE CAPT LEVELED OFF THE NOSE; BUT IT WAS NOT ENOUGH TO STOP THE CLB; RESULTING IN AN ALTDEV OF 800 FT (APPROX 3800 FT). ATC QUESTIONED OUR ALT AT THE SAME TIME THE CAPT WAS DECREASING THE PITCH AND STILL TRYING TO MAINTAIN BELOW 250 KTS. AFTER THE CORRECTION WAS MADE EVERYTHING SEEMED NORMAL; BUT WE WERE BOTH STILL CONFUSED AT WHAT OCCURRED. BOTH THE CAPT AND I HAD UNDER 100 HRS IN TYPE; BOTH BEING SO NEW IN THE ACFT AND TRYING TO FIGURE OUT CERTAIN COMPUTER UNDEMANDED COMMANDS DID NOT HELP THE SIT. 2 PLTS BOTH WITH LOW TIME IN TYPE SHOULD NOT BE PAIRED TOGETHER. TCASII IS NOT REQUIRED IN FREIGHT ACFT. HOWEVER; IF THIS EQUIP WAS INSTALLED; IT COULD HAVE GIVEN US NECESSARY AND PERTINENT INFO TO RESPOND HAD THERE BEEN A TFC CONFLICT.