If you looking for info regarding the 2.8 to 3.4 engine swap there is a lot of it on this bulletin board as well as ITOG. For starters the 3.4 engine comes from model year 93' to 95' Camaro or Firebird its also refered to as VIN "S". Provided that you have Auto transmission in your Trooper its a direct bolt-on application. On the outside it is virtually same engine with the exception of the starter which has to be swaped over to the driver side for Isuzu application.
Most of the junk yards will have the type of engine or you can look on the net for it. Either way they range in price between 300 and 600 hundred $ depending on the condition of the engine. I myself got a cheaper one because am planning to rebuild it from the ground up so I know what I got on the inside but you may want to just get a newer power plant so all you have to do is install it.
No matter how you look at it is a great upgrade for the tired old 2.8, it will actually provide the truck with an adequate power it should've come with form the begining. Highly recomended modification.
If you want some more info on the subject look around in the old posting on this site or e-mail me and I'll send you some of the stuff I got from other guys.
Happy hunting,

ElBarto.