rear end drag

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Hello everyone
In last few weeks I have been putting time and money into my 67 el camino
I have put in my 700r trans , love it ,& and also I had my 10 bolt rearend rebuilt ,I had everything done posi ,373 gears and etc ,after I put it in ,I feel that El co does not run as strong as when it had stock rearend in ,( 273 one legged ) feels like it drags , when I let off gas I hear a humming noise ,, could the 373 be too much for ten bolt ? Or is it that just bad gears ?any clue or suggestions ?