SF340 AVOIDING TSTM HAS ALTDEV NEAR DTW.

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WE WERE ON VECTORS TO JOIN THE 006 DEG RADIAL DXO. THE CTLS WERE XFERRED TO FO FOR ENRTE FLYING. FLYING HDG 030 DEGS TO JOIN. THIS WOULD TAKE US INTO A LEVEL 3 ECHO. HDG OF 050 DEGS TO JOIN WAS REQUESTED BY US AND QUICKLY DENIED. WE HAD BEGUN THE TURN TO 050 DEGS; BUT IMMEDIATELY STOPPED WHEN TOLD TO DO SO. AT THIS POINT THE HSI SCALE WAS SET TO 5 NM FOR RADAR IDENT OF ECHOES. ANY COURSE DEVS APPEARED TO BE LARGE; SO A LARGE CORRECTION WAS PROMPTLY MADE TO A HDG OF 330 DEGS. AT NO TIME DID WE GO W OF THE 006 DEG RADIAL. AT THIS POINT; WE WERE ESTABLISHED ON THE RADIAL. THE CTLR GAVE US A WARNING THAT WE WERE W OF COURSE AND NEEDED TO EXECUTE AN IMMEDIATE L TURN TO 180 DEGS. HE WAS VERY EXCITED; STEPPED ON ALL OF OUR XMISSIONS TO REPLY. AT NO TIME DID OUR INSTS INDICATE WE WERE W OF COURSE. WE INITIATED THE L TURN AND HEARD THE CTLR ISSUE A DSCNT TO 3000 FT. WE THOUGHT IT WAS FOR US AND WE COMPLIED. WE READ BACK ALT AND ATC CORRECTED US AND TOLD US TO MAINTAIN 4000 FT. THE ALT WAS NOT FOR US. WE HAD MADE IT TO 3600 FT BEFORE HDG BACK TO 4000 FT. ATC THEN VECTORED US TO A 030 DEG HDG TO INTERCEPT THE 006 DEG RADIAL; WHICH WE DID AT 4000 FT. THE PRESENCE OF CONVECTIVE ACTIVITY; THE XFER OF CTLS FROM CAPT TO FO; AND THE EXCITEMENT OF ATC ARE ALL FACTORS THAT LED TO THIS DEV. CORRECTIONS WERE PROMPTLY MADE AND ADHERENCE TO THE FLT PLAN WAS FOLLOWED AT ALL TIMES.