My 1995 Mazda B2300 Truck, 2-dr. 4cyl. When driving up hills mostly, it engine sounds like it's dieseling, loses power, and the oil gauge goes crazy. Help?

CHECK FILTERS YET?

YOU in UK and have a LORRY (means truck , in ROTW)
EDC 3776 electronics Diesel controller , engine lost power up a hill, sure.
No truck makers name?
no year truck
what size engine/? diesel?
lost power is :
1: bad fuel
2: filters dirty or packed up.
3: injectors clogged.
4: weak pumps.
5: other problems with EDC , scanned and seen,
6: truck needs service. or hill too tall./? IDK I can not see the hill.

Rod and main bearings are shot. Time for another engine, if you really like this old truck.

Did you ever change the fuel pump? most of the time when fuel pump is weak does that on hills, and then is hard to restart

If the check engine light is not on, it could be a restriction in the exhaust or mechanical problem with the truck.
If your model has a fan clutch on the water pump, it may not be working correctly.

replace the clutch master and save cylinders

Exhaust Converter -worn out & blocked?

Did you check fuel pressure while driving,
gauge taped to windshield

If you go thru the entire car testing as you
go ,you will find the problem

That said you most likely don't have the
knowledge or tools to do so

What your reffering to is 1=1000rpm, 2=2000rpm, etc.

Sounds like you are losing power due to possibly wear on the engine; being a 1995 model, I bet it has lots of miles on it.

Your motor is probably just wore out and needs replaced or rebuilt.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

oil pump sounds like it maybe scavenging for oil ,check oil level, oilpressure----how long since filter was changed? youdoit

My guess is injectors. The early duramax's had a lot of injector problems. They sometimes get to where they bleed constantly, and sometimes they break off... bad stuff. Check your oil for diesel. When my dads injectors when out on his 01 D'Max, his truck would run ok for a while, then lose power. Computer will cut power when it picks up an injector problem. BTW, Sightseer, diesels dont have spark plugs, however, the diesel filter is a good idea, you have to change them pretty regularly on the D'Max engines ( in order to try and prolong the injectors lives, mainly, the smallest bit of junk in your fuel can screw those early injectors up quick) I think they got the injectors mostly straightened out in the 04 models, what I've heard is thats the best model Duramax there has been, fuel economy, power, and reliability. Too bad all the year models arent that way :/