99 gmc jimmy 4.3 liter. hesitates and bogs down when giving it gas in first three gears, runs decent at higher speeds. it has trouble making it up hills and downshifts too easily. tranmission was rebuilt three months ago.
engine vaccum is a steady 18 in. at idle. replaced all plugs, fuel filter, air filter, egr valve, mass airflow sensor. problem persists. please help