Shifting problems TH400

Only a 2WD but someone might help...
'87 chevy pickup C10 (old body style), V6, TBI, TH400 Transmission. Low mileage truck... 95K Km (60K miles?).
Things seemed to be fine (I've only had the truck a month) till I floored it
and brought it up to hi-way speed last week, then...
Best described as late shifting. In fact I almost have to let off the gas to have it shift. Then as I feed it gas it seems to want to drop down to 2nd all the time. This is at city driving speeds.
Flooring it at a crawl speed (say after turning a corner at a stop sign) produces no 'kickdown' and certainly no eye popping acceleration (but it is a V6, full size 1/2 ton) -haven't tried it at a faster speed.
I changed the modulator (easy to do and was hoping). No change.
I figure the 'kickdown' is the fault of maybe the switch or solenoid but that should not have anything to do with standard smooth, timely shifting right? Isn't it just an on/off type thing?
Speaking of the Detent Switch, my Chilton Manual (horrible by the way) thinks it's on the gas pedal bracket. It is not. It must be on the throttle body... there is what looks like a switch (3 wires on it) on the right side. I'm not sure if this is it tho.
I also got a 'code 45'... "ECM has detected a rich exhaust condition". This was within 50 miles of the incident. I get that code every day now at varying times but usually within 15 minutes of driving.
I popped a vacuum gauge on it and it seems OK but I'm not sure what I should be looking for with that gauge. Some one gave me a tip on checking the vacuum for the code 45.
Thanks for any ideas,
--
Dave





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Could be the gov. too. Larry

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Sounds like the motor has a problem (hence the 02 rich) which is causing the engine to want to hang on to 2nd gear. She isn't going to give you 3rd if the vacuum to the modulator is all boogered up by a poor running engine. Likely the 02 sensor; I'd start there.
Doc

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. . ======== ======== snipped-for-privacy@hotmail.com (SoundsLikeAPorsche) cried out in forum:
Only a 2WD but someone might help...
'87 chevy pickup C10 (old body style), V6, TBI, TH400 Transmission. Low mileage truck... 95K Km (60K miles?).
Things seemed to be fine (I've only had the truck a month) till I floored it and brought it up to hi-way speed last week, then...
Best described as late shifting. In fact I almost have to let off the gas to have it shift.
Then as I feed it gas it seems to want to drop down to 2nd all the time. This is at city driving speeds.
Flooring it at a crawl speed (say after turning a corner at a stop sign) produces no 'kickdown' and certainly no eye popping acceleration (but it is a V6, full size 1/2 ton) -haven't tried it at a faster speed.
I changed the modulator (easy to do and was hoping). No change.
I figure the 'kickdown' is the fault of maybe the switch or solenoid but that should not have anything to do with standard smooth, timely shifting right? Isn't it just an on/off type thing? Speaking of the Detent Switch, my Chilton Manual (horrible by the way) thinks it's on the gas pedal bracket. It is not. It must be on the throttle body... there is what looks like a switch (3 wires on it) on the right side. I'm not sure if this is it tho. I also got a 'code 45'... "ECM has detected a rich exhaust condition". This was within 50 miles of the incident. I get that code every day now at varying times but usually within 15 minutes of driving. I popped a vacuum gauge on it and it seems OK but I'm not sure what I should be looking for with that gauge. Some one gave me a tip on checking the vacuum for the code 45. Thanks for any ideas,
--
Dave
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