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Hard shifting

93 GMC pickup, V8, automatic, 160,000 miles. occasionally 3 things happen at once…idle speed goes up, service engine soon light comes on, truck shifts at much higher speed from first to second than normal and shift is extremely hard. next day back to normal. this has happened 3 times in last 1000 miles. ideas?

When was your last transmission fluid change?

Look for vacuum leaks.

The answer is hiding behind that service engine soon light. As a '93 your is an OBD-1 system and today’s code readers can’t read our error codes.

But you should be able to do it yourself:

possibly never. i got the truck 3 years ago w/ 150,000 miles and no maintenance history. it’s on my to-do list. but the fluid is full and appears clean.

ah, very cool. will probably be next weekend before i get to it but i will check it out. where is the data link connector likely to be?