MD80 FO IS PERPLEXED THAT THE CAPTAIN FAILED TO TAKE APPROPRIATE FOLLOW-UP ACTION WHEN THE ACFT APPEARED TO CLEARLY BE MORE HEAVY THAN DOCUMENTED FOR TKOF.

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DURING INITIAL CLBOUT FROM ORD; FLAPS UP AND ACCELERATING; FMA DISPLAYED 'ALPHA SPD' UNTIL REF BUG SET TO 264 KTS. TPS SHOWED CLEAN MINIMUM MANEUVER SPD AS 253 KTS. WE SUSPECTED A POSSIBLE OVERWT TKOF DUE TO THE CONDITIONS ABOVE AND INTERPOLATING PERFORMANCE DATA FROM THE OPS MANUAL. TKOF ROLL SEEMED SLOWER THAN USUAL AS DID THE ROTATION. CLB TO CRUISE WAS UNEVENTFUL BUT WE CHOSE TO FLY AT FL280 INSTEAD OF FL320 DUE TO RIDE CONDITIONS AND WT. WE DID EVENTUALLY CLB TO FL320 BUT NEVER TO FL340 AS PLANNED. I MENTIONED TO THE CAPT THAT WE SHOULD CALL DISPATCH AND HAVE THEM WEIGH THE CARGO BUT HE THOUGHT I WAS JUST KIDDING AND DIDN'T THINK OUR COMPANY DID THAT SORT OF THING. I FAILED TO PRESS THE ISSUE; ERROR #1; BE CONFIDENT IN THE THINGS YOU KNOW YOU KNOW AND SPEAK UP. WE DISCUSSED THE POSSIBLE OVERWT CONDITION FURTHER BUT NEVER PUT IT IN THE LOGBOOK NOR CONTACTED DISPATCH. WE ALSO NEVER ENTERTAINED THE IDEA THAT IF WE WERE OVERWT ON TKOF; WE WOULD BE OVERWT ON LNDG; ERROR #2; LET OTHERS IN ON THE SECRET; THE MORE HEADS THE BETTER; DISPATCH MAY HAVE BEEN THE LINK TO TELL THE CAPT ABOUT WEIGHING THE CARGO. DISPATCH MAY HAVE ALSO REMINDED US ABOUT ADDING SPD FOR APCH AND LNDG OR BURNING DOWN FUEL. THE CAPT SAID DURING CRUISE THAT AFTER WE LANDED HE WOULD CALL DISPATCH AND DISCUSS IT WITH THEM; ERROR #3; THIS IS WHAT MAINT DOES. DON'T WAIT TILL LATER TO WRITE IT UP THEN HAVE TO DO A REPORT AFTER A 19 HR DAY. MY DEEPEST APOLOGY TO THE CREW AND PAX THAT HAD TO ENDURE OUR MESS. HAD WE SPOKEN UP SOONER; THE CARGO COULD HAVE BEEN WEIGHED; MAINT STARTED ON AN INSPECTION AND A SHORTER DAY WOULD HAVE FOLLOWED.