Strange trouble: engine or trans?

[Architectgal]

I have a 2002 chevrolet Tracker 4 door LT 4WD with 2.5 V6 and the automatic trans. 138,000 miles and up until last week seemingly near perfect. I service all regularly, but bought at 108,000 miles and do not know how the car's life was before me.

Trouble is that intermittantly in first gear (4 speed auto w/ OD 4th and lock up torque converter) the car sloggs. . .
1. With light throttle there is no problem
2. Under heavier throttle - as accelerating from stop or near stop with no one ahead of me - the car feels as though there is no power being produced
3. When this happens the shift: 1-2 occurs at only about 3500 RPM
4. Acceleration is slower with majpr throttle than with light throttle
5. Feels rather like an olden engine having a carb trouble
6. As soon as 1-2 upshift complete car takes off like it always did
7. shifts seem a bit slow when under throttle
8. Intermittantly gives two distinct bumps, not one, when moving from one trans position to another (P to D or R, R to D, D to R) at stop
9. Fluid about year old and just beginning to turn amber, not too bad
10. No error codes - no check engine light
11. Trans shop used their Snap On device to analyze car under 35 mile test and concluded issue like carboned intake manifold, thought not trans
12. My spanner spinner thinks trans
13. But in any case - why only in 1st?
14. Electronic? what?

thanx for your help!

[jtgh]

it is a slush pump. ( not fun)
you need to find out, is my tranny good or bad?

so , lock it in gear. id say 1st gear.
so, now you have no shifting going on ( and on the 4sp , the tcm ,when pulled turns the automatic into a manual , PULL TCM puter (if a 2002 has one, your on wrong forum and i do not have data on it) [fsm shows this proc. up to 98]

so , In 1st gear. we drive on road, and test
and we drive against foot on brake. test.
we do the stall test. and look at rpm.
is it normal.? on road, accelerate in 1st , up a steep hilll, not to fast just hit 4000rpm and say to sell , is this full power?
i think stall test in drive way is more effective.

is motor bogging.?
or
is tranny messing up. (slippage ,flare, noise. etc)

does tranny flare ?
or is it only shifting late or too early. ( if motor dont make power ,shifting will be off)

id say, see if you can get it to fail , in 1st gear. locked in to 1st.

if car does not flare ( slipping tranny ) then motor is bad (or EFI)

OBD2:
so put on the scan tool and drive and look at AFR mix.

look at all parameters and see that all are ok. hot, and running.
no codes ,dont mean its good.

just means nothing gross? did you look at pending codes. (soft fails are important)
does OBD2 show, TPS and MAF responses as normal.
and short term fuel trim normal ranges.

if not , maf could be bad. maf it trickiest of all to test.
good ones , go to 100 Grams a second (IIRC) on v6. ( my 1.6L goes to 60 max)
but bad ones , are (or worse weak) are impossible to test on car.

off car piece of cake. to test MAF. ( must have flow bench)

the bad maf , succumbs to the chicken and egg syndrome.
cant make max air, if maf is bad, and cant test maf, if i cant get to max air.(perplexing)

do you have a TCM? 2002? FSM for 2002 would be handy to say the least.

transmission control module in upper center dash , on some.?

cheers