Losing power on hills

Hi, everyone. New here, so if this question has already been answered, I apologize.
I have a 93 s10 blazer, 4.3 litre 'W', 4 door, 4wd Automatic Transmission. Bought it early this year, and it had 146,000 on it, and I now have 153,000 on it.
Runs and starts great, but loses power on hills at highway speeds. When you kick the gas a bit, it will downshift and chug up the hill at about 2500rpms. Seems to shift just fine any other time. No clunking or hard shifts.
Have replaced cpi unit (but not nut kit), new cap, rotor, and plug wires and plugs, new tranny filter and fluid.
Oil and filter changed every 3000 miles. Typical oil pressure around 50lbs or up.
I am wondering if it could be vacuum issue, as I also hear a vacuum leak in my heater controls, or maybe the catalytic converter? Or is this normal?? No check engine light, no odd noises. 4wd works great, (encoder motor, all switches, actuator, and cable new) and it will climb hills all day in the woods and mud at slower speeds...just seems to be highway speeds that cause this.
HELP!
It's a great rig in great condition, and I want to keep it forever!

could be the converter, hif the temp is rising than check it out

Hi, everyone. New here, so if this question has already been answered, I apologize.
I have a 93 s10 blazer, 4.3 litre 'W', 4 door, 4wd Automatic Transmission. Bought it early this year, and it had 146,000 on it, and I now have 153,000 on it.
Runs and starts great, but loses power on hills at highway speeds. When you kick the gas a bit, it will downshift and chug up the hill at about 2500rpms. Seems to shift just fine any other time. No clunking or hard shifts.
Have replaced cpi unit (but not nut kit), new cap, rotor, and plug wires and plugs, new tranny filter and fluid.
Oil and filter changed every 3000 miles. Typical oil pressure around 50lbs or up.
I am wondering if it could be vacuum issue, as I also hear a vacuum leak in my heater controls, or maybe the catalytic converter? Or is this normal?? No check engine light, no odd noises. 4wd works great, (encoder motor, all switches, actuator, and cable new) and it will climb hills all day in the woods and mud at slower speeds...just seems to be highway speeds that cause this.
HELP!
It's a great rig in great condition, and I want to keep it forever!

To ckeck for restricted exhaust hook a vacuum gauge to engine and see if vacuum at 2K is higher or lower that at idle
If lower you have restricted exhaust.
Post back gauge readings.

To ckeck for restricted exhaust hook a vacuum gauge to engine and see if vacuum at 2K is higher or lower that at idle
If lower you have restricted exhaust.
Post back gauge readings.

Dumb question: Should I check it at the vacuum line cluster at the back of the intake, or somewhere else?
And, I greatly appreciate the input!

Dumb question: Should I check it at the vacuum line cluster at the back of the intake, or somewhere else?
And, I greatly appreciate the input!

Any place that has good engine/intake vacuum.

Any place that has good engine/intake vacuum.

Great....will borrow (or buy) a guage tomorrow and test it out and post readings at idle and 2K!