A PIPER CHEROKEE PLT WAS GIVEN HIS LNDG CLRNC BY GRR TRACON.

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AT ABOUT XA50; I WAS APCHING CONVECTIVE WX/TSTMS ALONG MY RTE OF FLT. I WAS ON AN IFR FLT PLAN FROM YIP TO MKG. I ADVISED GRAND RAPIDS APCH THAT I WANTED TO DIVERT TO GRR. THE CTLR CLRED ME TO GRR AND TO MAINTAIN 4000 FT MSL. I ACKNOWLEDGED THE CLRNC AND RECEIVED RADAR VECTORS FOR RWY 26L. I WAS GIVEN A VECTOR AND CLRED TO INTERCEPT THE LOC FOR RWY 26L. AFTER INTERSECTING THE LOC INBOUND FOR RWY 26L; I WAS ADVISED TO KEEP MY SPD UP DUE TO JET TFC BEHIND ME. I WAS THEN CLRED FOR THE ILS RWY 26L GRR. I ACCEPTED THE CLRNC AND BEGAN MY DSCNT FROM 4000 FT MSL. I WAS HIGH ON THE GS DUE TO HAVING TO REMAIN AT 4000 FT MSL INSTEAD OF 2700 FT MSL DEPICTED ON THE APCH PLATE. ON SHORT FINAL; I QUERIED APCH ON WHETHER I SHOULD SWITCH TO TWR AND CONFIRM THAT I WAS CLRED TO LAND. APCH CLRED ME TO LAND AND TO CONTACT TWR ON THE ROLLOUT. AFTER LNDG; I CONTACTED THE TWR AND PROCEEDED TO PARKING. THE WORKLOAD FOR MYSELF AND ATC WAS INTENSE DUE TO BAD WX AND APCHING TSTMS. BOTH MYSELF AND ATC WERE RUSHED AND MISTAKES WERE MADE ON BOTH SIDES. IN THE FUTURE; STICKING TO SOP'S AND MAINTAINING POSITIVE COM COULD MINIMIZE ERRORS.