I have a Nissan terrano 3.0turbo diesel manual . Has lack of power in third and fourth gear

Wikipedia is usually the best way to check this as it gives good information on versions and generations.

Terrano - Wikipedia

Wikipedia https://en.wikipedia.org > wiki > Terrano
Terrano may refer to: Nissan Frontier, a pickup truck; Nissan Terrano, a sport utility vehicle; Nissan Mistral (Terrano II), a sport utility vehicle ...

NISSAN Terrano 5 Doors Models by Year (1990-Present)

autoevolution https://www.autoevolution.com > Cars > NISSAN

Dec 7, 2022 - Complete timeline of NISSAN Terrano 5 Doors models and generations, with photos, specs reference and production years.

what heater do you mean?
rear defrost
seat heates
or dash Blower heater dead? blower and or heat ? to cab>
ALL the DIESEL GLOW plugs are dead
that means they must be repaired, means get it serviced

1. check all fuses first.
2. scan the TDI PCM brain for why it fails.
3. or get it serviced.

try youtube

What is the problem? Do you need power mode which delays up shifts?

the Nissan td27 t is a gear driven unit

Probably you might face a problem on the injection pump with the Advance or retar positioning,and I believe that is controlled by the vehicle ECU. The Diesel Knocking you receive should be this fault.

Go and have the computer scanned for codes. Go from there, otherwise you are just firing the parts cannon at the problem.....

Possibly the "Mass airflow sensor". I had a similar problem, basically the car behaved like it didn't have a turbo and was really slow. Unfortunately the Mass airflow sensor is expensive, about AU$800. Only failed once several years ago. Hope this helps.

could be bent or loose selectors

some black smoke comes out when i put foot down and loses power when goiong uphill i have a nissan mistral/terrano 2.7td