My 2003 GMC Envoy xl SLE has no power on hills or when accelerating. Only one code being thrown P1345. Just Replaced Muffler and Resonator with OEM Parts. New Oil Chg and Filter. also replaced A/C Compressor with OEM Part. When hooked to "Reader" it shows 32.5% Load @ 823 RPM and 100% Load @ 2,500 RPM not towing anything, just driving. Maybe Cat. Conv. needs replacing? Please Help!