1998 Jimmy seems to skip when Air Conditioner is on
If it is running hotter with the A/C on then you need to check for air flow blockage through the front end cooling, ie bad fan clutch, crud in evap or radiator, bad coolant flow in the radiator. As far as the jump, you are most likely feeling the compressor turning on and during operation, as your engine gets older it looses power so an engine load that you just barely felt you now can really feel.
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