If I am on the interstate traveling 70 and hit a hill, by the time I get to the top of the hill I've dropped to 60. Full throttle doesn't help anymore. Just got the a/c working this year so I haven't had it on when the power loss began, however, when I hit the hill the a/c quickly diverts to the defrost outlets on top of the dash. I seem to be burning more fuel too. For the trucks 100k birthday, I changed out the plugs, flushed the radiator, changed the serp belt, and of course, gave her a new a/c system. All this after the loss started. Any troubleshooting things I should try? Any ideas as to what could be causing this? Thanks in advance.
Stuart

98 Ram 1500 5.2L

 

Is is just on the highway at high speeds? There are a lot of threads of loss of power and accelerating if you search for it.

This is a thread I started about loss of power that members gave me a lot of good information.
https://dodgeforum.com/m_777069/tm.htm

 

these trucks tend to drop off speed some on hills, but ...

lack of throttle response points to throttle position sensor (TPS). mine sort of did that where i'd hit a hill and press the gas a little and it seemed like nothing would happen. i'd press it more and still nothing would happen. i'd press it more and eventually the TV (kickdown) cable would cause a downshift and it rev up and shift a couple times and then upshift again and still be a dog. new tps is about $45 at your local auto parts. it helped mine a lot. do a search on tps for lots and lots of posts. its a common problem.

your second problem, ac/defrost, might (or might not) also be related to your lack of power. the switch from htr/ac to defrost indicates a loss of vacuum to the ac controls. presence of vacuum is required to open the door and blow through the front/lower vents. if you loose vacuum on the ac controls, the door will close and switch to defrost. do a search on 'defrost' and 'check valve'. the check valves are litte things in the vac line on passenger side near firewall. could be the check valve(not related to power loss), or could also be a straight forward split, loose vac line (which would contribute to problem #1 power loss)

 

I forgot to mention that the a/c will kick back to the correct vents if I let off the gas peddle. I have had to downshift to fourth gear to get up hills while 90 year old ladies pass me by. Maybe I should get a Buick! This problem started about two months ago. I was wondering if there might be a problem in the intake manifold since the a/c was door was shutting due to no vacuum. I'll look into the TPS, thanks.

 

The a/c problem is definately a weak check valve. Period. It would not have anything to do with the loss of power. I would tend to agree with dhvaughan about the TPS. Or possibly a restriction in exhaust/intake system. How is she running? Rough under power? Idle? Might also want to try a fuel pressure check.

 

To test the bad CAT theory, I removed the O2 sensor from the cat and the truck ran worse - 0 to 20 in like 20 seconds. I did like the noise during idle times tho! Making me think about a new exhaust system. Gonna try replacing the TPS this weekend. Wondering what WayneC was talking about with the "possibly a restriction in exhaust/intake system." Only because I lose vacuum pressure to the a/c when I try to apply more pedal to get the beast to move.

 

With a weak check valve to the a/c system it doesn't take much pedal to lose vacuum there completely. The more you try to accelerate the less vacuum you will have available to hold the vent doors open and the system will default into the defroster vents. When you let up on the pedal the vacuum returns to a point that the check valve starts to hold again and the air is then returned to the dash outlets. This can occur on level ground or when climbing a hill. Any time more power is called for. I've even seen it happen with a strong headwind! Try a new check valve.
Regarding a possible restriction in the intake/exhaust system I was referring to either the cat. or maybe loaded air filter or something along those lines. You may also want to test/replace the O2 sensor. It may be on the way out too and cause sluggish operation.
WC

 

My truck does the same thing.

AC vent changes to defroster under a load above medium.

Truck looses power on hills of the smaller size. Even with Full throttle on many hills it will not hold speed. New IAC, TPS, Wires, plugs, free flowing cat, good muffler. I think MAP or Fuel Pump. With the free flowing cat and hooker muffler I should hear the exhaust get louder when under a load. Crazy thing is sound doesn't increase and possibly gets quiter - under 100% throttle!

 

also my old plugs were worn but no signs of oil from plenumn leaks.

 

Removing the o2 sensor will only check the cat if it is badly clogged and hardly runs or won't run at all. It needs a backpressure test or atleast a thermal test. And since it's a 98, and the original cat as far as you know, it's bad or going bad. And you'll want to check the plenum also.